http://informahealthcare.com/drd ISSN: 1071-7544 (print), 1521-0464 (electronic) Drug Deliv, 2014; 21(6): 397–405 ! 2014 Informa Healthcare USA, Inc. DOI: 10.3109/10717544.2013.868555
ORIGINAL ARTICLE
Budesonide dry powder for inhalation: effects of leucine and mannitol on the efficiency of delivery Teerarat Rattanupatam1 and Teerapol Srichana1,2 Department of Pharmaceutical Technology and 2Nanotec-PSU Drug Delivery System Excellence Center, Faculty of Pharmaceutical Sciences, Prince of Songkla University, Hat Yai, Songkhla, Thailand
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1
Abstract
Keywords
Objective: The aim of this study was to develop a budesonide dry powder for inhalation using L-leucine and L-leucine – sieved mannitol as a carrier. Materials and methods: Budesonide and L-leucine were co-spray dried at a mass ratio of 1:50 then blended with various mass ratios of sieved mannitol in the range of 20–80. A 23 factorial study was applied to investigate the effects of the spray drying variables; feed rate, aspirator setting and airflow rate on the powder characteristics. The prepared dry powders were characterized using fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and ultracentrifugation. Drug contents and aerosolization properties were evaluated using high performance liquid chromatography (HPLC) and the Andersen cascade impactor (ACI), respectively. Results and discussion: There was no interaction between budesonide and L-leucine after co-spraying. The budesonide dry powders had a mass median aerodynamic diameter (MMAD) in the range of 1.9–2.2 mm at a flow rate of 60 L/min that was suitable for pulmonary delivery. Sieved mannitol as a coarse carrier decreased the interparticulate forces between fine particles of the co-spray dried budesonide-L-leucine and resulted in a high fine particle fraction (FPF) in the range of 64–68% while the co-spray dried powder of budesonide-L-leucine had an FPF of 49%. Conclusions: Blending of the co-spray dried powder with sieved mannitol significantly improved the delivery efficiency of the micronized budesonide better than the co-spray dried with L-leucine alone.
Adhesion force, aerosolization, antiinflammatory, carrier, spray dried powder
Introduction Budesonide is a potent non-halogenated corticosteroid with a high ratio of topical anti-inflammatory to systemic activity. When administered directly to the lung it has prolonged airway retention and is well tolerated by all ages of patients. It inhibits inflammatory symptoms such as edema and vascular hyperpermeability (Szefler, 1999; El-Gendy et al., 2008). The major problem of orally administered budesonide is its low bioavailability (6–13%) due to its extensive first-pass metabolism in the liver (Szefler, 1999). Therefore the development of budesonide for direct delivery to the lung could provide many advantages. Furthermore, inhaled glucocorticosteroids are recommended as the first-line therapy for asthma and as an inhaled drug it acts locally, and a relatively lower dose can be employed resulting in lower systemic side effects (Szefler, 1999; Naikwade et al., 2009). Dry powder inhaler (DPI) systems are becoming popular for delivering drugs directly into the airway because they are Address for correspondence: Dr Teerapol Srichana, Department of Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand. Tel: +66 74 288 842. Fax: +66 74 288 148. Email: [email protected]
History Received 21 September 2013 Revised 18 November 2013 Accepted 19 November 2013
portable, do not require coordination of inhalation with device actuation and the formulation of the drug as a dry powder offers a potential for improved stability during storage (Rabbani & Seville, 2005; Telko & Hickey, 2005; Sou et al., 2011). For effective deposition in the lower airways and deep into the lung, the aerodynamic diameter of the particles needs to be in a range of 1–5 mm, however, powders in this size range normally exhibit strong interparticulate cohesion, leading to manufacturing problems, dose variability, with poor flowability and aerosolization (Rabbani & Seville, 2005; Jones et al., 2008). Several strategies (Pilcer & Amighi, 2010) including excipient systems have seemed to improve the flowability and consequently the aerosolization properties of dry powders, known as carrier-based DPIs (Rabbani & Seville, 2005; Seville et al., 2007). Current excipients approved for pulmonary drug delivery are limited to a few sugars such as lactose, mannitol and glucose as these reduce the cohesive forces of micronized drugs (Pilcer & Amighi, 2010). Amino acids that are co-spray dried with a few other active compounds have been demonstrated to improve the drug aerosolization performance. They also had been a decreased hygroscopicity, improved surface activity and a change in the
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density of the particles. L-leucine was especially able to improve drug aerosolization properties (Seville et al., 2007; Pilcer & Amighi, 2010; Prota et al., 2011). Pulmicort TurbuhalerÕ (AstraZeneca, Lund, Sweden), a commercial product, is a multi-dose DPI that has been widely used for the delivery of budesonide powder. However, it has been reported that the amount of drug delivered from the TurbuhalerÕ varied greatly from dose to dose and the fine particle dose was reduced significantly when used with a low inspiratory flow rate (Hirst et al., 2002). Several studies have attempted to improve the aerosolization properties of budesonide DPI such as by changing the budesonide particle to nanoporous microparticles (Nolan et al., 2009), agglomerated nanoparticles (El-Gendy et al., 2008), microspheres and porous particles (Naikwade et al., 2009) and ultra-fine particles by antisolvent precipitation (Hu et al., 2008) or mixing with other excipients such as L-leucine (Boraey et al., 2012). All of these studies have reported that the aerosolization properties of the modified dry powders can be improved when compared with untreated budesonide or spray dried budesonide alone. The co-spray dried budesonideleucine with a mass ratio of 82.5:17.5 (Boraey et al., 2012) that the dry powder needs to deliver 242 mg to be equivalent to 200 mg of budenoside. It is not very practical to weigh 242 mg of the dry powder and to fill into a capsule for inhalation delivery in a unit-dose device. We have developed a co-spray dried powder of budesonide with L-leucine as a carrier and demonstrated its dose homogeneity and a good aerosolization performance of the prepared DPI. However the prepared co-spray dried powder was very fine and remained as a highly cohesive powder. Hence, the purpose of this study was to improve the aerosolization performance of the co-spray dried budesonide-L-leucine diluted with sieved mannitol as a coarse carrier for inhalation delivery in a passive unit-dose DPI. Finally, the physiochemical properties and in vitro aerosolization of the prepared dry powders were evaluated.
Materials and methods Materials Micronized budesonide was from AeroCare Co., Ltd., Thailand. L-leucine was from Ajinomoto Co., Inc., Tokyo, Japan. D-mannitol was from Fluka Biochemika, Steinheim, Germany. Acetonitrile A.R., ethanol A.R. and methanol A.R. were from Lab-Scan Analytical Sciences, Thailand. Orthophosphoric acid 85% was from Merck, Germany and potassium dihydrogen orthophosphate was from Ajax Finechem Pty Ltd, Australia. Other chemicals of analytical grade were purchased from local suppliers in Thailand. Optimization of the spray drying process parameters The spray drying method enabled adjustment of many parameters, and an understanding of the process parameters was necessary to obtain the desired dried powder with a predictable performance (Tajber et al., 2009b). A 23 full factorial design was applied to investigate the effect of the main spray drying processing variables on the powder characteristics. The processing variables were (A) feed rate,
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Table 1. Spray drying process parameter. Parameter
Low ()
High (þ)
Units
Feed rate (A) Aspirator (B) Airflow (C) Inlet temperature Feed solution conc. Spray nozzle
5 (1.5) 70 (28) 437
15 (4.5) 90 (36) 742
% (mL/min) % (m3/h) L/h C % w/v mm
110 1.0 0.7
Table 2. The magnitude of the impact of each factor by calculation and Yates’s treatment (mean SD, n ¼ 3). Factor Experiment
A
B
C
Yield (%)
Magnitude
F (Yate’s test)
(1) a b ab c ac bc abc
þ þ þ þ
þ þ þ þ
þ þ þ þ
71.52 6.56 79.91 2.02 68.65 5.35 74.78 1.33 54.97 1.87 70.20 4.03 66.47 3.61 69.26 5.08
8.13a 0.64 3.68 8.49a 0.88 4.64 2.55
161.04a 32.94 175.62a 1.87 52.48 15.79
a
The main effect.
(B) aspirator setting and (C) airflow rate, using the Buchi Mini Spray Dryer B-290. Each factor was studied at two levels and other factors were fixed as listed in Table 1. Budesonide and L-leucine with a ratio of 1:150 was employed to optimize the spray drying conditions using 20% w/v of ethanol as a solvent. A low level of the effect of a factor was identified with a () sign and high level with a (þ) sign. The experimental set ups are shown in Table 2 and the response variables (production yield, drug content, particle size and Carr’s index) were measured. The magnitudes of the main effects of the factors and the interactions and Yates’s treatment for analysis of variation were calculated to examine the factors that had the main effects on the powder characteristics (Armstrong & James, 1990). The relationships between the main factors and interactions with the response were determined by multiple linear regressions and have been presented as the general form in the following equation: X X Y ¼ intercept þ main effects þ interactions Formulation design Dry powder formulations with various amounts of sieved mannitol in the ratio of 20, 50 and 80 were blended with the co-spray dried budesonide-L-leucine at a ratio of 1:50 (Formulations LM1, LM2 and LM3, respectively) as shown in Table 3. A co-spray of dried budesonide-L-leucine in a ratio of 1:50 was used as a control (Formulation L1). Each formulation contained 200 mg of budesonide. Preparation of co-spray dried powder and yield The co-spray drying method was used to prepare the co-spray dried powder of budesonide-L-leucine. It produced a composite powder with good dose homogeneity. A quantity of
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Table 3. Formulation parameter and response of a budesonide dry powder inhaler (mean SD, n ¼ 3). L-leucine
Formulation L1 LM1 LM2 LM3 Sieved mannitol
(mg)
Seived Mannitol (mg)
Weight per unit dose (mg)a
Bulk density (g/mL)
Tapped density (g/mL)
CI (%)
10 10 10 10
0 4 10 16
10.2 14.2 20.2 26.2
0.05 0.01 0.08 0.01 0.12 0.01 0.16 0.01 0.43 0.01
0.08 0.01 0.13 0.02 0.19 0.02 0.23 0.01 0.52 0.01
32.7 2.3 35.0 0.0 35.0 0.0 30.3 0.3 17.5 0.0
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CI ¼ Carr’s Index flowability: 5–12%, excellent; 12–18%, good; 18–21%, fair; 21–25%, poor, fluid; 25–32%, poor, cohesive; 32–38%, very poor; 440%, extremely poor (Seville et al., 2007). a Each formulation contained 200 mg of budesonide.
micronized budesonide and L-leucine was weighed and dissolved in ethanol and distilled water, respectively, and then mixed together with the solid content of 1% w/w and ethanol-distilled water with a ratio of 20:80 (v/v). The final solution was spray dried using the Buchi Mini Spray dryer B-290 (Switzerland) under the optimized spray drying conditions: inlet temperature, 110 C; airflow rate, 473 L/h; aspirator, 90% and pump rate, 6.0 mL/min. These conditions resulted in an outlet temperature of 45–49 C. Production yields were expressed as weight percentages of the final product over the total amount of the sprayed material. Preparation of powder blend D-mannitol
was sieved through a sieve analyzer with a sieve series of 90, 70 and 20 mm for 10 min. Mannitol retained on the 20 mm sieve was used to prepare the dry powder inhaler formulations. The dry powder inhalers were prepared by physical mixing between the co-spray dried powder of budesonide-L-leucine (in the ratio of 1:50) with sieved mannitol according to the ratios in Table 3, using a V-shaped mixing apparatus for 20 min. All formulations were collected and stored in a desiccator at room temperature. Particle size and size distribution The particle size of the sieved mannitol was measured by laser diffraction (Coulter LS230, Richmond Scientific Ltd., London, UK), using 1-butanol as the suspension medium. The particle size of the co-spray dried powder was determined by the Zetasizer Nano series (Malvern Instruments Ltd., UK), using 1butanol for measuring the size of the L-leucine and distilled water for measuring the size of the budesonide. All suspensions were sonicated for 2 min before measuring their sizes. Powder density and flowability The density and flowability of the DPI are presented in terms of bulk, tapped density and Carr’s Index, respectively. The bulk density was determined by pouring a known weight of powder under gravity into a calibrated measuring cylinder and the volume occupied by the powder was recorded. The tapped density of the same samples was subsequently determined using an automatic tapper for 500 times to displace the powder until no further change in the powder volume was observed (Naikwade et al., 2009). Measurements were performed in triplicate. The Carr’s
Index (CI) value of each spray dried powder was calculated according to Equation (1). Carr0 s Index ð% CIÞ ¼
ðTapped density Bulk densityÞ 100 Tapped density ð1Þ
Drug content and content uniformity The budesonide content in each DPI formulation was determined by high-performance liquid chromatography (HPLC) (ThermoÕ ) – UV spectrophotometry at a wavelength of 240 nm (British Pharmacopoeia, 2011). The mobile phase consisted of ethanol, acetonitrile and 25 mM phosphate buffer (pH 3.2) in a ratio of 2:35:65 (v/v), respectively. The system was isocratic at ambient temperature (25 C), a 50 mL injection volume and a flow rate of 1.5 mL/min with an ACEÕ HPLC column (length: 150 mm, diameter: 4.6 mm, ODS packing, particle size: 5 mm). The budesonide epimers B and A were eluted at 12 and 13 min, respectively. The calibration curve was prepared in a range of concentrations from 0.1 to 4.0 mg/mL. The content uniformity was expressed as the percentage of coefficient of variation (% CV). Fourier-transform infrared spectroscopy (FT-IR) Fourier transform-infrared spectra (Spectrum One, Perkin Elmer, Foster City, CA) were recorded with an FT functional group spectrometer to study the interaction between the drug and carrier molecules. Spectra in the range of 400–4000 cm1 and an accumulation of 16 scans were used. Samples were prepared by mixing with KBr in a ratio of 1:100 and compressed with 10 t of hydraulic press for 1–2 min. Thermal analysis The thermal behavior of the powders was investigated using the differential scanning calorimeter (DSC7, Perkin-Elmer) to prove drug–carrier compatibility in the DPI formulations. Samples of 2–3 mg were placed in an aluminum pan that was hermetically sealed. The sample was heated up to 350 C at a heating rate of 10 C/min in a nitrogen atmosphere. Determination of the drug–carrier detachment force The drug–carrier detachment force was determined by ultracentrifugation. The centrifuge tube was developed by adding a stainless steel tube inside a plastic centrifuge tube and sandwiching sieves (mean double sieves
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Figure 1. Drug–carrier detachment test by ultracentrifugation; (a) two tubes made up of steel were inserted in a plastic centrifuge tube and the double sieves was sandwiched in a middle of the two half cut tube and (b) diagram showing the experimental setup. The centrifuge tube was placed in the rotor of the centrifuge, the position of the powder on the sieves determining the radius of centrifugation (d). During centrifugation, a force (F), proportional to the angular velocity (!), will pull on the powder with an angle of 180 C.
size: 40 25 mm) in the middle of two halves of the tube as shown in Figure 1(a). The drug–carrier mixture from each formulation (equivalence to 100 mg of budesonide) was loaded into the upper portion of the tube. The tube was then put into the ultracentrifuge tube holder and centrifuged in the SW60Ti rotor, using the Ultracentrifuge (OptimaÔ L100 XP, Beckman Coulter, CA) at different g forces each at 25 C for 5 min. The centrifuge speeds were set at 7000, 9000, 12 000 and 15 000rpm equivalent to centrifugal forces or accelerations of 6600, 10 910, 19 400 and 30 300g (where g ¼ 9.82 m/s2), respectively. After being centrifuged, the drug that had separated from the carrier was carefully collected from the lower tube by washing it with 25 mL of the mobile phase used on the HPLC column and analyzed. The median g-force was defined as the g-force at 50% of the cumulative percentage of drug particles that were detached versus the Xg forces. The median g-force was employed to calculate the detachment force required to separate the drug from the carrier. This value was used to approximate the interaction between the drug and the carrier in the DPI formulations. The separation force or adhesion force between the co-spray dried powder and sieved mannitol was determined by the following Equations (2) and (3): (Lam & Newton, 1992; Felicetti et al., 2008) Fadhesion ¼ Fcentrifugal
ð2Þ
Fcentrifugal ¼ m!2 d
ð3Þ
The magnitude of the Fcentrifugal applied depended on the particle mass (m), given in kg; on the angular velocity (!) of the rotor, given in rad/s and on the distance between the particle and the rotation shaft (d) as shown in Figure 1(b). The distance between the particle and the rotation shaft was 0.082 m. The centrifugation frequency ƒc (rpm) was converted to an angular velocity (!) according to the following Equation (4): (Bailly et al., 2009). ! ¼ fc =30
ð4Þ
In vitro aerosolization of budesonide dry powder formulation The in vitro aerosolization of the dry powder inhaler was investigated using an Andersen Cascade Impactor (ACI) (Andersen Sampler, Inc., Atlanta, GA). The ACI comprises a pre-separator, then eight stages each with a collection plate. Stage cut-off diameters of stages 1, 0, 1, 2, 3, 4, 5 and 6 are 8.6, 6.5, 4.4, 3.2, 1.9, 1.2, 0.55 and 0.26 mm, respectively (Rabbani & Seville, 2005). The content of all DPI formulations were aerosolized into the ACI using the in-house plastic device at a flow rate of 60 L/min for 10 s (British Pharmacopoeia, 2011). After actuating a single dose into the ACI, the glass throat, pre-separator and each stage and collection plate was rinsed with either 10 or 25 mL of mobile phase as appropriate. The concentration of budesonide in each solution was determined by HPLC, from which the mass of the drug deposited on each stage and plate of the ACI was determined. The emitted dose (ED) was defined as a percentage of the total loaded powder mass propelled from the delivery device. The fine particle fraction (FPF) was defined as the amount of the drug deposited on stages 1–6 of the impactor with an aerodynamic diameter of 54.4 mm, as expressed as a percentage of the total dose delivered. The mass median aerodynamic diameter (MMAD) of the powders was defined as a particle size at a percentile of 50 of a plot of the cumulative fraction of the particles deposited on stages 1 to 6 of the ACI on the y axis against the effective cut-off diameter on the x axis (Rabbani & Seville, 2005; Prota et al., 2011). Statistical analysis Values are presented as a mean SD from at least three samples unless otherwise stated. One-way analysis of variance (ANOVA) was applied to compare mean results and the Student’s t-test were carried out for statistical comparisons. The differences were considered to be statistically significant when p values 50.05.
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Results and discussion
Particle size and size distribution
Optimization of the spray drying process parameter
The median particle size of the sieved mannitol that was retained on the 20 mm sieves was 53.85 34.16 mm. The mean particle sizes of the budesonide and L-leucine in the co-spray dried formulation were 0.19 0.02 mm and 1.60 0.04 mm with a poly disperse index (PdI) of 0.40 and 0.36, respectively.
The experimental methodology design was employed to systematically evaluate the effect of the feed rate, aspirator and airflow as well as for any interactions among these various factors on the production yield, drug content, particle size and the Carr’s index of the budesonide dry powder formulations. The resulting data obtained from the various responses showed no statistical difference among these parameters except on the percentage yield. Various processing variables caused considerable changes in the yield of the powder over a range from 55 to 80% (Table 2). The magnitudes of the main effects of the various factors and their interactions were calculated. For example, the magnitude of the factor A was the mean for all experiments with a high level of A, minus the mean of all those with a low level. Thus, the magnitude of factor A was 1 4{[aþabþacþabc][(1)þbþcþbc]}. The values of magnitude for the main effects and interactions are given in Table 2. They showed that the most important factors were the feed rate and airflow rate. Moreover, the values of F were calculated for the Yates’s treatment and assessed by comparing them with the tabulated values (Table 2). The numerator has one degree of freedom and the denominator has two, therefore for p50.01, F should be 498.5. Thus the feed rate and the airflow rate are clearly the two most important factors for the production yield. By multiple linear regressions, the relationships between the main factors; feed rate (A) and airflow rate (C) with the yield response have been presented as an Equation (5): Y ¼ 80:517 þ ð2:711 AÞ ð0:0316 CÞ
ð5Þ
When Y is the production yield, A is the feed rate and C is the airflow rate. From this equation, a positive parameter coefficient indicated that the output increased with increasing variable level and a negative coefficient indicated that the output increased with a decreasing variable level. The coefficient of the feed rate (A) was positive which meant that when the feed rate increased, a high production yield was obtained and the coefficient of the airflow rate (C) was negative which means that a low production yield was obtained when the airflow rate increased. Spray dried yield The dry powder of budesonide mixed with L-leucine was prepared by the co-spray drying method with optimized dry spray conditions. The yield of the recovered powder was 94%. Boraey et al. (2012) demonstrated that when a 100% budesonide formulation was spray dried using the Buchi 191 apparatus with a co-solvent ratio of 85% ethanol and 15% water, most of the powder was deposited on the wall surfaces of the cyclone and only 17% of the dry powder mass was recovered from the collector (Boraey et al., 2012). This indicated that using L-leucine in the formulation significantly decreased the cohesive force of the powder and consequently the low adhesion of the powder to the walls of the spray dryer that ultimately led to the high production yield.
Powder density and flowability From Table 3, the bulk density of the co-spray dried powder (Formulation L1) was 0.052 g/mL. Blending of the co-spray dried powders with various ratios of sieved mannitol resulted in an increase of the powder density over the range of 0.08– 0.16 g/mL whereas the sieved mannitol alone showed a bulk density of 0.43 g/mL. Although the co-spray dried powder showed a lower density than that of the formulations blended with sieved mannitol, the latter exhibited better aerosolization. In addition to the powder density, the adhesion force between the particles was also an important factor that affected the aerosol performance. Blending of the sieved mannitol with the co-spray dried powder was demonstrated to improve the aerosol performance by reducing the adhesion force between the co-spray dried powders. Boraey et al. (2012) suggested that the powder bulk density was a function of both the particle density and the particle packing behavior of which the latter was strongly affected by the cohesive force of the powder. A powder with a low tapped density exhibited low compressibility and was presented as a highly cohesive powder (Boraey et al., 2012). The blending of the sieved mannitol with the dried co-spray, thus, produced an increase in the tapped density caused by a decrease in the powder cohesion. The Carr’s index (CI), an indication of the powder flow properties, for all formulation was 425% and indicated poor flowability while the sieved mannitol exhibited good flowability with CI of 17.5% (Seville et al., 2007). In comparing the formulations LM1 to LM3, the use of sieved mannitol at a high ratio improved the flowability of the DPI formulations. Carrier flowability is known to affect the emission of a drug from a DPI device and possibly enhanced the delivery of that drug to the lungs (Jones et al., 2008). Drug content and content uniformity The drug content of formulations LM1 to LM3 was between 86 and 89% (Table 5). All of this was within the criteria of the British pharmacopoeia that specified a value of 80–120% (British Pharmacopoeia, 2011). All formulations provided a percentage of coefficient of variation (CV) 56%, which is a value commonly taken as sufficiently uniform for DPI systems (Table 5) (Beilmann et al., 2007; Jones et al., 2008). Fourier transform-infrared spectroscopy (FT-IR) There are many functional groups such as amine, carboxylic, hydroxyl and carbonyl groups in the structures of L-leucine and budesonide that can form hydrogen bonding between these molecules and affect the detachment of the drug–carrier during aerosolization. Hence the drug–carrier interaction was investigated by FT-IR. The IR spectrum of budesonide showed carbonyl stretching at 1723 and 1667 cm1 (Figure 2c). The first carbonyl stretching peak at 1723 cm1
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Figure 2. IR spectrum of (a) kneaded budesonide-L-leucine at a ratio of 1:1, (b) spray dried L-leucine and (c) micronized budesonide.
Figure 3. Thermogram of (a) spray dried L-leucine, (b) micronized budesonide, (c) co-spray dried budesonide-L-leucine at a ratio of 1:50 and (d) kneaded budesonide-L-leucine at a ratio of 1:1.
belonged to the non-conjugated acetyl C ¼ O vibrations and the second peak at 1667 cm1 was the conjugated dihydrobenzenoquinone C ¼ O. This was similar to the findings of Tajber et al. (2009a) and the OH bands appeared as a broad peak located in the 3300–3700 cm1 region. The IR spectrum of the spray dried L-leucine showed carbonyl stretching bands at 1528 cm1 (Figure 2b). Furthermore the IR spectrum of the kneaded budesonide-L-leucine in a ratio of 1:1 (Figure 2a) showed all the carbonyl stretching bands of budesonide and the spray dried L-leucine and indicated that there was no chemical interaction between budesonide and L-leucine when they were kneaded together. Thermal analysis Budesonide was supplied as a micronized powder and the DSC analysis of this powder confirmed the crystalline nature of the starting material as only one endothermic peak at 260 C was observed (Figure 3b) as well as an endothermic
peak of the spray dried L-leucine at 300 C (Figure 3a). Spray dried budesonide was demonstrated to be amorphous (Tajber et al., 2009a; Boraey et al., 2012) and Tajber et al. (2009a) reported that a glass transition (Tg) and a recrystallization exotherm was seen in the thermogram of the spray dried budesonide with a peak at 89.5 C and 130 C, respectively, and this was followed by a melting endotherm with a peak at 262 C (Tajber et al., 2009a). The high glass transition temperatures of these amorphous samples indicated a good physical stability when stored at room temperature (Nolan et al., 2009). Consequently the endothermic peak at 280 C was seen in the thermogram of the co-spray dried budesonideL -leucine in the ratio of 1:50 (Figure 3c) and this may result from the shifted melting point of the spray dried L-leucine alone and the peaks were more diffuse as a result of losing the ordering of the crystal lattice. The exotherm was not seen in the thermogram of the co-spray dried budesonide-L-leucine (a ratio of 1:50) due to the eutectic mixture that may form followed by a glass transition and a recrystallization. A twophase solid-liquid system was formed and it was composed of a liquid phase (budesonide in L-leucine) and a pure solid L -leucine to form a mixed crystal (Martin et al., 1993). This indicated that budesonide was amorphous in the co-spray dried powder which was useful for enhancing its solubility and the dissolution properties of the insoluble drug that would improve their pulmonary absorption. Figure 3(d) shows the thermogram of the kneaded budesonide-L-leucine in a ratio of 1:1. One endothermic peak at 215 C was observed and that may result from the shifted melting point of budesonide. It was noticed that the endothermic peak of L-leucine was not seen in this thermogram due to the formation of a eutectic mixture. Determination of the drug–carrier detachment force Drug adhesion to the carrier can be influenced by the surface of the drug and carrier, the drug to carrier ratio, the carrier
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Table 5. Drug content, coefficient of variation (CV) and in vitro aerosolization properties of the dry powders (mean SD, n 3).
Formulation L1 LM1 LM2 LM3
Content (%)a
CV (%)
ED (%)
FPF (%)
MMAD (mm)
GSD
93.7 1.9 93.0 2.4 92.6 1.8 94.7 1.6
1.99 2.78 2.39 1.81
73.8 2.8 75.6 1.2 77.2 2.4 76.6 1.0
49.4 3.2 67.7 1.0 67.4 1.9 64.3 3.8
2.24 0.11 1.86 0.04 1.94 0.07 2.09 0.10
3.30 0.05 2.93 0.01 2.90 0.03 2.92 0.05
a
n ¼ 5. ED, emitted dose; FPF, fine particle fraction; MMAD, mass median aerodynamic diameter, GSD, geometric standard deviation.
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detachment during aerosolization (Schiavone et al., 2004; Telko & Hickey, 2005). Figure 4. Drug–carrier detachment forces of budesonide dry powder inhalers (Formulations L1, LM1, LM2 and LM3) by ultracentrifugation (mean SD, n ¼ 3).
Table 4. Adhesion force of formulations L1, LM1, LM2 and LM3 at 50% of drug detachment (mean SD, n ¼ 3).
Formulation L1 LM1 LM2 LM3
Adhesion force (mN) At 50% of drug detachment (SD) 5.25 0.10 4.77 0.04 3.98 0.26 3.55 0.28
particle size the mixing time and method, the amount of moisture and the electrostatic behavior (Schiavone et al., 2004; Beilmann et al., 2007). The median g-force was used to approximate the interaction between the co-spray dried powder and the sieved mannitol in the DPI formulations as shown in Figure 4. The drug–carrier detachment profiles changed when we changed the type of a carrier and the drug to carrier ratio. The co-spray dried powder of budesonideL-leucine blended with the sieved mannitol (Formulations LM1 to LM3) had a much lower median g-force than that of the co-spray dried budesonide-L-leucine alone (Formulation L1). Furthermore with formulations of LM1 to LM3 with different ratios of sieved mannitol, the formulation LM3 with the highest ratio of sieved mannitol showed the lowest median g-force compared to the other two formulations. The median adhesion force can be defined as the adhesion force at which there is a 50% probability that the drug particles separate through the sieves after centrifugation. It can be calculated by the regression equation obtained from the log-probability plots of the percentage of drug detachment versus the Xg-force. The calculated results of the median adhesion force of all formulations are shown in Table 4. The results of the median adhesion force correlated with the results of the median g-force, i.e. the formulation blended with the sieved mannitol exhibited a lower median adhesion force than that of the co-spray dried budesonide-L-leucine alone. It was clear that using sieved mannitol as a coarse carrier decreased the adhesion force between the budesonide and the carriers. The adhesion force must be sufficient to avoid demixing during metering but small enough to allow for
In vitro powder aerosolization The in vitro aerosolization and deposition of the DPI formulations has been summarized in Table 5. The ED, FPF and MMAD indicated the effectiveness of the aerosol performance. The percentages of ED for all formulations were not statistically different, in the range of 74–77% of the dose contents released during aerosolization. The MMAD obtained during aerosolization of all formulations were varied between 1.9 and 2.2 mm all of which were suitable for pulmonary drug delivery. The MMAD of the formulations blended with sieved mannitol had a lower MMAD than the co-spray dried formulation, but it was not statistically different when compared with the formulation LM3. In a similar manner, the FPF of the co-spray dried powder of budesonide-L-leucine was statistically (p value 50.05) lower than the FPF of the co-spray dried powder blended with sieved mannitol (Table 5). The co-spray dried powder blended with sieved mannitol showed better aerosolization properties with an FPF in the range of 64–68% while the co-spray dried powder of budesonide-L-leucine had the FPF of 49%. The geometric standard deviation (GSD) or an aerodynamic particle size spread of all DPI formulations was in the range of 2.9–3.3 (Table 5), and thus were polydisperse powders. The co-spray dried powder of budesonide-L-leucine was prone to behave as a high powder aggregation due to interparticulate forces between the fine particles. An uncontrolled powder aggregation led to variations of the sizes of the agglomerates resulting in polydisperse powders. The formulation blended with sieved mannitol exhibited a decrease in the GSD due to the better powder dispersibility. However, after aerosolization the fine particles were separated from the coarse carrier, while some of them were able to aggregate again. Typical GSD values for the aerosol particles were between 1.3 and 3.0 (El-Gendy et al., 2008). In comparison, the co-spray dried powder of budesonide-Lleucine blended with sieved mannitol had a FPF of 64–68% while Nolan et al. (2009) demonstrated that the FPF of the micronized budesonide carried out on the Pulmicort 400 mg TurbuhalerÕ at a flow rate of 58 L/min was 53% with an MMAD of 2.9 mm (Nolan et al., 2009). It was clear that the co-spray dried powder of budesonide-L-leucine blended with sieved mannitol showed better aerosolization than that of the commercial product with a higher FPF and a lower MMAD. Hence the DPI formulation of the co-spray dried
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budesonide-L-leucine blended with the sieved mannitol could potentially lead to a reduction in the prescribed dose of budesonide without reducing therapeutic efficacy. Micronized particles are often highly charged and cohesive, resulting in significant downstream processing and poor product performance (Schiavone et al., 2004). Addition of L-leucine to a dry powder inhaler has been demonstrated to improve the aerosolization properties of the micronized drug by the formation of a crystalline L-leucine shell around the active pharmaceutical ingredient during the evaporation of droplets that resulted in a reduction of the cohesive forces and improved powder dispersion (Boraey et al., 2012). However, using a high amount of L-leucine as the lone carrier by cospray dried with micronized drug, the co-spray dried powders were fine so they exhibited powder cohesion. The blending of mixtures of micronized drug particles that adhered to the surface of the coarse carrier particles has been employed to reduce the cohesion forces between the primary drug particle (Schiavone et al., 2004; Beilmann et al., 2007). Moreover, the blend systems significantly enhanced drug particle flowability, thus improving the dosing accuracy and minimizing the dose variability observed with neat drug formulations and making them easier to handle during the manufacturing operations (Schiavone et al., 2004). Hence the blending of the sieved mannitol as a coarse carrier into the co-spray dried powder of budesonide-L-leucine reduced the interparticulate forces between the micronized powders and consequently, these dry powders behaved as low powder aggregates leading to a high FPF. Furthermore, it was confirmed by the drug–carrier detachment test that for the formulations of LM1 to LM3 and L1, the median adhesion forces of the formulation LM1 to LM were in the range of 3.6–4.8 mN and were lower than that of the formulation L1 (5.3 mN). This indicated that the adhesion force of the co-spray dried powder was reduced when sieved mannitol was added. The drug deposition profile of formulations L1 and LM1 are shown in Figure 5, and both formulations travelled as far as the final stage of the ACI. Although formulation LM1 retained in the device higher than that of formulation L1, the percentage of ED of both were not statistically different. Formulation LM1 demonstrated good dispersibility with a high deposition on stage 2, 3 and 4 of the ACI resulting in a higher FPF than that of formulation L1. While the DPI formulations were aerosolized through the device, the blending of the sieved mannitol with the co-spray dried powder was demonstrated to reduce the cohesive force between the micronized particles with low powder aggregation. Whereas the co-spray dried powder alone significantly deposited higher in the pre-separator which reduced the particle fraction deposited on the impactor stages and resulted in a lower FPF. This could be due to the presence of particle agglomerates. Previous studies have reported that the blending ratio of the carrier can impact aerosol performance. Schiavone et al. (2004) suggested that the excess drug particles could possibly mitigate strong binding carrier–drug and carrier–carrier interactions, thus allowing for more efficient aerosolization (Schiavone et al., 2004). Hamishehkar et al. (2010) demonstrated that the deposition profiles of PLGA microcapsules with higher carrier ratio caused a lower FPF of microcapsules.
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Figure 5. Drug deposition after aerosolization of formulations L1 (white bars) and LM1 (dark bars) into the Andersen cascade impactor at an air flow rate of 60 L/min (mean SD, n ¼ 3).
This result may also be attributed to the ‘‘hot spot theory’’ that indicates that a high drug load in the mix occupies the active sites on the carrier surface and enables the remaining drug particles to adhere at the low energy sites to be more easily detached (Steckel et al., 2004). However, there was no effect of the blending ratio on the FPF (p value40.05) among the formulations LM1 to LM3, although the drug–carrier detachment results showed that an increase of the ratio of the sieved mannitol produced a lower drug–carrier adhesion force (in the same amount of powder load). For in vitro powder aerosolization, all factors were controlled to produce a similar condition, except the amount of the powder load for each formulation. During inhalation, the drug particles were detached from the carrier particle surface by the energy of the inhalation flow. It was possible that using a high amount of the powder load might reduce the shearing force of the airflow that affected the powder aerosolization.
Conclusions Although the co-spray dried powder of budesonide mixed with a high amount of L-leucine, as a carrier, can be prepared with an appropriate aerodynamic size for pulmonary delivery the co-spray dried powder was prone to aggregation due to interparticulate forces between the fine particles that resulted in a reduction of the dispersibility during inhalation. The blending of sieved mannitol, as a coarse carrier, with the cospray dried budesonide-L-leucine had a high FPF, an improved in vitro deposition property compared to the cospray dried powder alone, and that was attributed to improvement of the aerosolization due to the reduced interparticulate forces of the co-spray dried powder. The mass ratio of the sieved mannitol at 20–80 blended with the co-spray dried powder of budesonide-L-leucine (at a ratio of 1:50) provided good aerosolization performance with the FPF of 64–68% that was higher than the FPF of the commercial product (Pulmicort 400 mg TurbuhalerÕ ). It is therefore postulated that those formulations would deliver the majority of the ED to the lower stage of ACI via a passive single-unit dose device with minimal deposition on the pre-separator and stage that would significantly reduce the amount of the drug reaching the bronchi.
DOI: 10.3109/10717544.2013.868555
Acknowledgements The authors would like to thank Dr Brian Hodgson for editing the manuscript.
Declaration of interest This work was supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission, Graduate School, Prince of Songkla University and Nanotec-PSU Excellence Center on Drug Delivery System. The authors report no declaration of interest.
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References Armstrong NA, James KC. (1990). Understanding experimental design and interpretation in pharmaceutics. West Sussex: Ellis Horwood Limited. Bailly P, Grosjean P, Flammang P. (2009). Measurement of the attachment strength of brachiolaria larvae and metamorphic individuals of the sea star Asterina gibbosa by a centrifugation method. J Exp Mar Biol Ecol 372:82–90. Beilmann B, Kubiak R, Grab P, et al. (2007). Effect of interactive ternary mixtures on dispersion characteristics of ipratropium bromide in dry powder inhaler formulations. AAPS PharmSciTech 8:E32–9. Boraey MA, Hoe S, Sharif H, et al. (2012). Improvement of the dispersibility of spray-dried budesonide powders using leucine in an ethanol-water cosolvent system. Powder Technol 236:171–8. British Pharmacopoeia. (2011). London: British Pharmacopoeial Commission. El-Gendy N, Gorman EM, Munson EJ, Berkland C. (2008). Budesonide nanoparticle agglomerates as dry powder aerosols with rapid dissolution. J Pharm Sci 98:2731–46. Felicetti MA, Piantino F, Coury JR, Aguiar ML. (2008). Influence of removal time and particle size on the particle substrate adhesion force. Braz J Chem Eng 25:71–82. Hamishehkar H, Emami J, Najafabadi AR, et al. (2010). Influence of carrier particle size, carrier ratio and addition of fine ternary particles on the dry powder inhalation performance of insulin-loaded PLGA microcapsules. Powder Technol 201:289–95. Hirst PH, Newman SP, Clark DA, Hertog MGL. (2002). Lung deposition of budesonide from the novel dry powder inhaler AirmaxÔ. Respir Med 96:389–96. Hu TT, Zhao H, Jiang LC, et al. (2008). Engineering pharmaceutical fine particles of budesonide for dry powder inhalation (DPI). Ind Eng Chem Res 47:9623–7.
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Jones MD, Harris H, Hooton JC, et al. (2008). An investigation into the relationship between carrier-based dry powder inhalation performance and formulation cohesive-adhesive force balances. Eur J Pharm Biopharm 69:496–507. Lam KK, Newton JM. (1992). Influence of particle size on the adhesion behaviour of powders, after application of an initial press-on force. Powder Technol 73:117–25. Martin A, Bustamante P, Chun AHC. (1993). Physical pharmacy. Philadelphia: Lea & Febiger. Naikwade SR, Bajaj AN, Gurav P, et al. (2009). Development of budesonide microparticles using spray-drying technology for pulmonary administration: design, characterization, in vitro evaluation, and in vivo efficacy study. AAPS PharmSciTech 10:993–1012. Nolan LM, Tajber L, McDonald BF, et al. (2009). Excipient-free nanoporous microparticles of budesonide for pulmonary delivery. Eur J Pharm Sci 37:593–602. Pilcer G, Amighi K. (2010). Formulation strategy and use of excipients in pulmonary drug delivery. Int J Pharm 392:1–19. Prota L, Santoro A, Bifulco M, et al. (2011). Leucine enhances aerosol performance of Naringin dry powder and its activity on cystic fibrosis airway epithelial cells. Int J Pharm 412:8–19. Rabbani NR, Seville PC. (2005). The influence of formulation components on the aerosolisation properties of spray-dried powders. J Control Release 110:130–40. Schiavone H, Palakodaty S, Clark A, et al. (2004). Evaluation of SCFengineered particle-based lactose blends in passive dry powder inhalers. Int J Pharm 281:55–66. Seville PC, Learoyd TP, Li HY, et al. (2007). Amino acid-modified spray-dried powders with enhanced aerosolisation properties for pulmonary drug delivery. Powder Technol 178:40–50. Sou T, Orlando L, McIntosh MP, et al. (2011). Investigating the interactions of amino acid components on a mannitol-based spraydried powder formulation for pulmonary delivery: a design of experiment approach. Int J Pharm 421:220–9. Steckel H, Markefka P, teWierik H, Kammelar R. (2004). Functionality testing of inhalation grade lactose. Eur J Pharm Biopharm 57: 495–505. Szefler SJ. (1999). Pharmacodynamics and pharmacokinetics of budesonide: a new nebulized corticosteroid. J Allergy Clin Immun 104:S175–83. Tajber L, Corrigan DO, Corrigan OI, Healy AM. (2009a). Spray drying of budesonide, formoterol fumarate and their composites-I. Physiochem charecterisation. Int J Pharm 367:79–85. Tajber L, Corrigan OI, Healy AM. (2009b). Spray drying of budesonide, formoterol fumarate and their composites-II. Statistical factorial design and in vitro deposition properties. Int J Pharm 367:86–96. Telko MJ, Hickey AJ. (2005). Dry powder inhaler formulation. Respir Care 50:1209–27.
ORIGINAL ARTICLE
Budesonide dry powder for inhalation: effects of leucine and mannitol on the efficiency of delivery Teerarat Rattanupatam1 and Teerapol Srichana1,2 Department of Pharmaceutical Technology and 2Nanotec-PSU Drug Delivery System Excellence Center, Faculty of Pharmaceutical Sciences, Prince of Songkla University, Hat Yai, Songkhla, Thailand
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1
Abstract
Keywords
Objective: The aim of this study was to develop a budesonide dry powder for inhalation using L-leucine and L-leucine – sieved mannitol as a carrier. Materials and methods: Budesonide and L-leucine were co-spray dried at a mass ratio of 1:50 then blended with various mass ratios of sieved mannitol in the range of 20–80. A 23 factorial study was applied to investigate the effects of the spray drying variables; feed rate, aspirator setting and airflow rate on the powder characteristics. The prepared dry powders were characterized using fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and ultracentrifugation. Drug contents and aerosolization properties were evaluated using high performance liquid chromatography (HPLC) and the Andersen cascade impactor (ACI), respectively. Results and discussion: There was no interaction between budesonide and L-leucine after co-spraying. The budesonide dry powders had a mass median aerodynamic diameter (MMAD) in the range of 1.9–2.2 mm at a flow rate of 60 L/min that was suitable for pulmonary delivery. Sieved mannitol as a coarse carrier decreased the interparticulate forces between fine particles of the co-spray dried budesonide-L-leucine and resulted in a high fine particle fraction (FPF) in the range of 64–68% while the co-spray dried powder of budesonide-L-leucine had an FPF of 49%. Conclusions: Blending of the co-spray dried powder with sieved mannitol significantly improved the delivery efficiency of the micronized budesonide better than the co-spray dried with L-leucine alone.
Adhesion force, aerosolization, antiinflammatory, carrier, spray dried powder
Introduction Budesonide is a potent non-halogenated corticosteroid with a high ratio of topical anti-inflammatory to systemic activity. When administered directly to the lung it has prolonged airway retention and is well tolerated by all ages of patients. It inhibits inflammatory symptoms such as edema and vascular hyperpermeability (Szefler, 1999; El-Gendy et al., 2008). The major problem of orally administered budesonide is its low bioavailability (6–13%) due to its extensive first-pass metabolism in the liver (Szefler, 1999). Therefore the development of budesonide for direct delivery to the lung could provide many advantages. Furthermore, inhaled glucocorticosteroids are recommended as the first-line therapy for asthma and as an inhaled drug it acts locally, and a relatively lower dose can be employed resulting in lower systemic side effects (Szefler, 1999; Naikwade et al., 2009). Dry powder inhaler (DPI) systems are becoming popular for delivering drugs directly into the airway because they are Address for correspondence: Dr Teerapol Srichana, Department of Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand. Tel: +66 74 288 842. Fax: +66 74 288 148. Email: [email protected]
History Received 21 September 2013 Revised 18 November 2013 Accepted 19 November 2013
portable, do not require coordination of inhalation with device actuation and the formulation of the drug as a dry powder offers a potential for improved stability during storage (Rabbani & Seville, 2005; Telko & Hickey, 2005; Sou et al., 2011). For effective deposition in the lower airways and deep into the lung, the aerodynamic diameter of the particles needs to be in a range of 1–5 mm, however, powders in this size range normally exhibit strong interparticulate cohesion, leading to manufacturing problems, dose variability, with poor flowability and aerosolization (Rabbani & Seville, 2005; Jones et al., 2008). Several strategies (Pilcer & Amighi, 2010) including excipient systems have seemed to improve the flowability and consequently the aerosolization properties of dry powders, known as carrier-based DPIs (Rabbani & Seville, 2005; Seville et al., 2007). Current excipients approved for pulmonary drug delivery are limited to a few sugars such as lactose, mannitol and glucose as these reduce the cohesive forces of micronized drugs (Pilcer & Amighi, 2010). Amino acids that are co-spray dried with a few other active compounds have been demonstrated to improve the drug aerosolization performance. They also had been a decreased hygroscopicity, improved surface activity and a change in the
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density of the particles. L-leucine was especially able to improve drug aerosolization properties (Seville et al., 2007; Pilcer & Amighi, 2010; Prota et al., 2011). Pulmicort TurbuhalerÕ (AstraZeneca, Lund, Sweden), a commercial product, is a multi-dose DPI that has been widely used for the delivery of budesonide powder. However, it has been reported that the amount of drug delivered from the TurbuhalerÕ varied greatly from dose to dose and the fine particle dose was reduced significantly when used with a low inspiratory flow rate (Hirst et al., 2002). Several studies have attempted to improve the aerosolization properties of budesonide DPI such as by changing the budesonide particle to nanoporous microparticles (Nolan et al., 2009), agglomerated nanoparticles (El-Gendy et al., 2008), microspheres and porous particles (Naikwade et al., 2009) and ultra-fine particles by antisolvent precipitation (Hu et al., 2008) or mixing with other excipients such as L-leucine (Boraey et al., 2012). All of these studies have reported that the aerosolization properties of the modified dry powders can be improved when compared with untreated budesonide or spray dried budesonide alone. The co-spray dried budesonideleucine with a mass ratio of 82.5:17.5 (Boraey et al., 2012) that the dry powder needs to deliver 242 mg to be equivalent to 200 mg of budenoside. It is not very practical to weigh 242 mg of the dry powder and to fill into a capsule for inhalation delivery in a unit-dose device. We have developed a co-spray dried powder of budesonide with L-leucine as a carrier and demonstrated its dose homogeneity and a good aerosolization performance of the prepared DPI. However the prepared co-spray dried powder was very fine and remained as a highly cohesive powder. Hence, the purpose of this study was to improve the aerosolization performance of the co-spray dried budesonide-L-leucine diluted with sieved mannitol as a coarse carrier for inhalation delivery in a passive unit-dose DPI. Finally, the physiochemical properties and in vitro aerosolization of the prepared dry powders were evaluated.
Materials and methods Materials Micronized budesonide was from AeroCare Co., Ltd., Thailand. L-leucine was from Ajinomoto Co., Inc., Tokyo, Japan. D-mannitol was from Fluka Biochemika, Steinheim, Germany. Acetonitrile A.R., ethanol A.R. and methanol A.R. were from Lab-Scan Analytical Sciences, Thailand. Orthophosphoric acid 85% was from Merck, Germany and potassium dihydrogen orthophosphate was from Ajax Finechem Pty Ltd, Australia. Other chemicals of analytical grade were purchased from local suppliers in Thailand. Optimization of the spray drying process parameters The spray drying method enabled adjustment of many parameters, and an understanding of the process parameters was necessary to obtain the desired dried powder with a predictable performance (Tajber et al., 2009b). A 23 full factorial design was applied to investigate the effect of the main spray drying processing variables on the powder characteristics. The processing variables were (A) feed rate,
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Table 1. Spray drying process parameter. Parameter
Low ()
High (þ)
Units
Feed rate (A) Aspirator (B) Airflow (C) Inlet temperature Feed solution conc. Spray nozzle
5 (1.5) 70 (28) 437
15 (4.5) 90 (36) 742
% (mL/min) % (m3/h) L/h C % w/v mm
110 1.0 0.7
Table 2. The magnitude of the impact of each factor by calculation and Yates’s treatment (mean SD, n ¼ 3). Factor Experiment
A
B
C
Yield (%)
Magnitude
F (Yate’s test)
(1) a b ab c ac bc abc
þ þ þ þ
þ þ þ þ
þ þ þ þ
71.52 6.56 79.91 2.02 68.65 5.35 74.78 1.33 54.97 1.87 70.20 4.03 66.47 3.61 69.26 5.08
8.13a 0.64 3.68 8.49a 0.88 4.64 2.55
161.04a 32.94 175.62a 1.87 52.48 15.79
a
The main effect.
(B) aspirator setting and (C) airflow rate, using the Buchi Mini Spray Dryer B-290. Each factor was studied at two levels and other factors were fixed as listed in Table 1. Budesonide and L-leucine with a ratio of 1:150 was employed to optimize the spray drying conditions using 20% w/v of ethanol as a solvent. A low level of the effect of a factor was identified with a () sign and high level with a (þ) sign. The experimental set ups are shown in Table 2 and the response variables (production yield, drug content, particle size and Carr’s index) were measured. The magnitudes of the main effects of the factors and the interactions and Yates’s treatment for analysis of variation were calculated to examine the factors that had the main effects on the powder characteristics (Armstrong & James, 1990). The relationships between the main factors and interactions with the response were determined by multiple linear regressions and have been presented as the general form in the following equation: X X Y ¼ intercept þ main effects þ interactions Formulation design Dry powder formulations with various amounts of sieved mannitol in the ratio of 20, 50 and 80 were blended with the co-spray dried budesonide-L-leucine at a ratio of 1:50 (Formulations LM1, LM2 and LM3, respectively) as shown in Table 3. A co-spray of dried budesonide-L-leucine in a ratio of 1:50 was used as a control (Formulation L1). Each formulation contained 200 mg of budesonide. Preparation of co-spray dried powder and yield The co-spray drying method was used to prepare the co-spray dried powder of budesonide-L-leucine. It produced a composite powder with good dose homogeneity. A quantity of
Budesonide dry powder for inhalation
DOI: 10.3109/10717544.2013.868555
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Table 3. Formulation parameter and response of a budesonide dry powder inhaler (mean SD, n ¼ 3). L-leucine
Formulation L1 LM1 LM2 LM3 Sieved mannitol
(mg)
Seived Mannitol (mg)
Weight per unit dose (mg)a
Bulk density (g/mL)
Tapped density (g/mL)
CI (%)
10 10 10 10
0 4 10 16
10.2 14.2 20.2 26.2
0.05 0.01 0.08 0.01 0.12 0.01 0.16 0.01 0.43 0.01
0.08 0.01 0.13 0.02 0.19 0.02 0.23 0.01 0.52 0.01
32.7 2.3 35.0 0.0 35.0 0.0 30.3 0.3 17.5 0.0
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CI ¼ Carr’s Index flowability: 5–12%, excellent; 12–18%, good; 18–21%, fair; 21–25%, poor, fluid; 25–32%, poor, cohesive; 32–38%, very poor; 440%, extremely poor (Seville et al., 2007). a Each formulation contained 200 mg of budesonide.
micronized budesonide and L-leucine was weighed and dissolved in ethanol and distilled water, respectively, and then mixed together with the solid content of 1% w/w and ethanol-distilled water with a ratio of 20:80 (v/v). The final solution was spray dried using the Buchi Mini Spray dryer B-290 (Switzerland) under the optimized spray drying conditions: inlet temperature, 110 C; airflow rate, 473 L/h; aspirator, 90% and pump rate, 6.0 mL/min. These conditions resulted in an outlet temperature of 45–49 C. Production yields were expressed as weight percentages of the final product over the total amount of the sprayed material. Preparation of powder blend D-mannitol
was sieved through a sieve analyzer with a sieve series of 90, 70 and 20 mm for 10 min. Mannitol retained on the 20 mm sieve was used to prepare the dry powder inhaler formulations. The dry powder inhalers were prepared by physical mixing between the co-spray dried powder of budesonide-L-leucine (in the ratio of 1:50) with sieved mannitol according to the ratios in Table 3, using a V-shaped mixing apparatus for 20 min. All formulations were collected and stored in a desiccator at room temperature. Particle size and size distribution The particle size of the sieved mannitol was measured by laser diffraction (Coulter LS230, Richmond Scientific Ltd., London, UK), using 1-butanol as the suspension medium. The particle size of the co-spray dried powder was determined by the Zetasizer Nano series (Malvern Instruments Ltd., UK), using 1butanol for measuring the size of the L-leucine and distilled water for measuring the size of the budesonide. All suspensions were sonicated for 2 min before measuring their sizes. Powder density and flowability The density and flowability of the DPI are presented in terms of bulk, tapped density and Carr’s Index, respectively. The bulk density was determined by pouring a known weight of powder under gravity into a calibrated measuring cylinder and the volume occupied by the powder was recorded. The tapped density of the same samples was subsequently determined using an automatic tapper for 500 times to displace the powder until no further change in the powder volume was observed (Naikwade et al., 2009). Measurements were performed in triplicate. The Carr’s
Index (CI) value of each spray dried powder was calculated according to Equation (1). Carr0 s Index ð% CIÞ ¼
ðTapped density Bulk densityÞ 100 Tapped density ð1Þ
Drug content and content uniformity The budesonide content in each DPI formulation was determined by high-performance liquid chromatography (HPLC) (ThermoÕ ) – UV spectrophotometry at a wavelength of 240 nm (British Pharmacopoeia, 2011). The mobile phase consisted of ethanol, acetonitrile and 25 mM phosphate buffer (pH 3.2) in a ratio of 2:35:65 (v/v), respectively. The system was isocratic at ambient temperature (25 C), a 50 mL injection volume and a flow rate of 1.5 mL/min with an ACEÕ HPLC column (length: 150 mm, diameter: 4.6 mm, ODS packing, particle size: 5 mm). The budesonide epimers B and A were eluted at 12 and 13 min, respectively. The calibration curve was prepared in a range of concentrations from 0.1 to 4.0 mg/mL. The content uniformity was expressed as the percentage of coefficient of variation (% CV). Fourier-transform infrared spectroscopy (FT-IR) Fourier transform-infrared spectra (Spectrum One, Perkin Elmer, Foster City, CA) were recorded with an FT functional group spectrometer to study the interaction between the drug and carrier molecules. Spectra in the range of 400–4000 cm1 and an accumulation of 16 scans were used. Samples were prepared by mixing with KBr in a ratio of 1:100 and compressed with 10 t of hydraulic press for 1–2 min. Thermal analysis The thermal behavior of the powders was investigated using the differential scanning calorimeter (DSC7, Perkin-Elmer) to prove drug–carrier compatibility in the DPI formulations. Samples of 2–3 mg were placed in an aluminum pan that was hermetically sealed. The sample was heated up to 350 C at a heating rate of 10 C/min in a nitrogen atmosphere. Determination of the drug–carrier detachment force The drug–carrier detachment force was determined by ultracentrifugation. The centrifuge tube was developed by adding a stainless steel tube inside a plastic centrifuge tube and sandwiching sieves (mean double sieves
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Drug Deliv, 2014; 21(6): 397–405
Figure 1. Drug–carrier detachment test by ultracentrifugation; (a) two tubes made up of steel were inserted in a plastic centrifuge tube and the double sieves was sandwiched in a middle of the two half cut tube and (b) diagram showing the experimental setup. The centrifuge tube was placed in the rotor of the centrifuge, the position of the powder on the sieves determining the radius of centrifugation (d). During centrifugation, a force (F), proportional to the angular velocity (!), will pull on the powder with an angle of 180 C.
size: 40 25 mm) in the middle of two halves of the tube as shown in Figure 1(a). The drug–carrier mixture from each formulation (equivalence to 100 mg of budesonide) was loaded into the upper portion of the tube. The tube was then put into the ultracentrifuge tube holder and centrifuged in the SW60Ti rotor, using the Ultracentrifuge (OptimaÔ L100 XP, Beckman Coulter, CA) at different g forces each at 25 C for 5 min. The centrifuge speeds were set at 7000, 9000, 12 000 and 15 000rpm equivalent to centrifugal forces or accelerations of 6600, 10 910, 19 400 and 30 300g (where g ¼ 9.82 m/s2), respectively. After being centrifuged, the drug that had separated from the carrier was carefully collected from the lower tube by washing it with 25 mL of the mobile phase used on the HPLC column and analyzed. The median g-force was defined as the g-force at 50% of the cumulative percentage of drug particles that were detached versus the Xg forces. The median g-force was employed to calculate the detachment force required to separate the drug from the carrier. This value was used to approximate the interaction between the drug and the carrier in the DPI formulations. The separation force or adhesion force between the co-spray dried powder and sieved mannitol was determined by the following Equations (2) and (3): (Lam & Newton, 1992; Felicetti et al., 2008) Fadhesion ¼ Fcentrifugal
ð2Þ
Fcentrifugal ¼ m!2 d
ð3Þ
The magnitude of the Fcentrifugal applied depended on the particle mass (m), given in kg; on the angular velocity (!) of the rotor, given in rad/s and on the distance between the particle and the rotation shaft (d) as shown in Figure 1(b). The distance between the particle and the rotation shaft was 0.082 m. The centrifugation frequency ƒc (rpm) was converted to an angular velocity (!) according to the following Equation (4): (Bailly et al., 2009). ! ¼ fc =30
ð4Þ
In vitro aerosolization of budesonide dry powder formulation The in vitro aerosolization of the dry powder inhaler was investigated using an Andersen Cascade Impactor (ACI) (Andersen Sampler, Inc., Atlanta, GA). The ACI comprises a pre-separator, then eight stages each with a collection plate. Stage cut-off diameters of stages 1, 0, 1, 2, 3, 4, 5 and 6 are 8.6, 6.5, 4.4, 3.2, 1.9, 1.2, 0.55 and 0.26 mm, respectively (Rabbani & Seville, 2005). The content of all DPI formulations were aerosolized into the ACI using the in-house plastic device at a flow rate of 60 L/min for 10 s (British Pharmacopoeia, 2011). After actuating a single dose into the ACI, the glass throat, pre-separator and each stage and collection plate was rinsed with either 10 or 25 mL of mobile phase as appropriate. The concentration of budesonide in each solution was determined by HPLC, from which the mass of the drug deposited on each stage and plate of the ACI was determined. The emitted dose (ED) was defined as a percentage of the total loaded powder mass propelled from the delivery device. The fine particle fraction (FPF) was defined as the amount of the drug deposited on stages 1–6 of the impactor with an aerodynamic diameter of 54.4 mm, as expressed as a percentage of the total dose delivered. The mass median aerodynamic diameter (MMAD) of the powders was defined as a particle size at a percentile of 50 of a plot of the cumulative fraction of the particles deposited on stages 1 to 6 of the ACI on the y axis against the effective cut-off diameter on the x axis (Rabbani & Seville, 2005; Prota et al., 2011). Statistical analysis Values are presented as a mean SD from at least three samples unless otherwise stated. One-way analysis of variance (ANOVA) was applied to compare mean results and the Student’s t-test were carried out for statistical comparisons. The differences were considered to be statistically significant when p values 50.05.
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Results and discussion
Particle size and size distribution
Optimization of the spray drying process parameter
The median particle size of the sieved mannitol that was retained on the 20 mm sieves was 53.85 34.16 mm. The mean particle sizes of the budesonide and L-leucine in the co-spray dried formulation were 0.19 0.02 mm and 1.60 0.04 mm with a poly disperse index (PdI) of 0.40 and 0.36, respectively.
The experimental methodology design was employed to systematically evaluate the effect of the feed rate, aspirator and airflow as well as for any interactions among these various factors on the production yield, drug content, particle size and the Carr’s index of the budesonide dry powder formulations. The resulting data obtained from the various responses showed no statistical difference among these parameters except on the percentage yield. Various processing variables caused considerable changes in the yield of the powder over a range from 55 to 80% (Table 2). The magnitudes of the main effects of the various factors and their interactions were calculated. For example, the magnitude of the factor A was the mean for all experiments with a high level of A, minus the mean of all those with a low level. Thus, the magnitude of factor A was 1 4{[aþabþacþabc][(1)þbþcþbc]}. The values of magnitude for the main effects and interactions are given in Table 2. They showed that the most important factors were the feed rate and airflow rate. Moreover, the values of F were calculated for the Yates’s treatment and assessed by comparing them with the tabulated values (Table 2). The numerator has one degree of freedom and the denominator has two, therefore for p50.01, F should be 498.5. Thus the feed rate and the airflow rate are clearly the two most important factors for the production yield. By multiple linear regressions, the relationships between the main factors; feed rate (A) and airflow rate (C) with the yield response have been presented as an Equation (5): Y ¼ 80:517 þ ð2:711 AÞ ð0:0316 CÞ
ð5Þ
When Y is the production yield, A is the feed rate and C is the airflow rate. From this equation, a positive parameter coefficient indicated that the output increased with increasing variable level and a negative coefficient indicated that the output increased with a decreasing variable level. The coefficient of the feed rate (A) was positive which meant that when the feed rate increased, a high production yield was obtained and the coefficient of the airflow rate (C) was negative which means that a low production yield was obtained when the airflow rate increased. Spray dried yield The dry powder of budesonide mixed with L-leucine was prepared by the co-spray drying method with optimized dry spray conditions. The yield of the recovered powder was 94%. Boraey et al. (2012) demonstrated that when a 100% budesonide formulation was spray dried using the Buchi 191 apparatus with a co-solvent ratio of 85% ethanol and 15% water, most of the powder was deposited on the wall surfaces of the cyclone and only 17% of the dry powder mass was recovered from the collector (Boraey et al., 2012). This indicated that using L-leucine in the formulation significantly decreased the cohesive force of the powder and consequently the low adhesion of the powder to the walls of the spray dryer that ultimately led to the high production yield.
Powder density and flowability From Table 3, the bulk density of the co-spray dried powder (Formulation L1) was 0.052 g/mL. Blending of the co-spray dried powders with various ratios of sieved mannitol resulted in an increase of the powder density over the range of 0.08– 0.16 g/mL whereas the sieved mannitol alone showed a bulk density of 0.43 g/mL. Although the co-spray dried powder showed a lower density than that of the formulations blended with sieved mannitol, the latter exhibited better aerosolization. In addition to the powder density, the adhesion force between the particles was also an important factor that affected the aerosol performance. Blending of the sieved mannitol with the co-spray dried powder was demonstrated to improve the aerosol performance by reducing the adhesion force between the co-spray dried powders. Boraey et al. (2012) suggested that the powder bulk density was a function of both the particle density and the particle packing behavior of which the latter was strongly affected by the cohesive force of the powder. A powder with a low tapped density exhibited low compressibility and was presented as a highly cohesive powder (Boraey et al., 2012). The blending of the sieved mannitol with the dried co-spray, thus, produced an increase in the tapped density caused by a decrease in the powder cohesion. The Carr’s index (CI), an indication of the powder flow properties, for all formulation was 425% and indicated poor flowability while the sieved mannitol exhibited good flowability with CI of 17.5% (Seville et al., 2007). In comparing the formulations LM1 to LM3, the use of sieved mannitol at a high ratio improved the flowability of the DPI formulations. Carrier flowability is known to affect the emission of a drug from a DPI device and possibly enhanced the delivery of that drug to the lungs (Jones et al., 2008). Drug content and content uniformity The drug content of formulations LM1 to LM3 was between 86 and 89% (Table 5). All of this was within the criteria of the British pharmacopoeia that specified a value of 80–120% (British Pharmacopoeia, 2011). All formulations provided a percentage of coefficient of variation (CV) 56%, which is a value commonly taken as sufficiently uniform for DPI systems (Table 5) (Beilmann et al., 2007; Jones et al., 2008). Fourier transform-infrared spectroscopy (FT-IR) There are many functional groups such as amine, carboxylic, hydroxyl and carbonyl groups in the structures of L-leucine and budesonide that can form hydrogen bonding between these molecules and affect the detachment of the drug–carrier during aerosolization. Hence the drug–carrier interaction was investigated by FT-IR. The IR spectrum of budesonide showed carbonyl stretching at 1723 and 1667 cm1 (Figure 2c). The first carbonyl stretching peak at 1723 cm1
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Figure 2. IR spectrum of (a) kneaded budesonide-L-leucine at a ratio of 1:1, (b) spray dried L-leucine and (c) micronized budesonide.
Figure 3. Thermogram of (a) spray dried L-leucine, (b) micronized budesonide, (c) co-spray dried budesonide-L-leucine at a ratio of 1:50 and (d) kneaded budesonide-L-leucine at a ratio of 1:1.
belonged to the non-conjugated acetyl C ¼ O vibrations and the second peak at 1667 cm1 was the conjugated dihydrobenzenoquinone C ¼ O. This was similar to the findings of Tajber et al. (2009a) and the OH bands appeared as a broad peak located in the 3300–3700 cm1 region. The IR spectrum of the spray dried L-leucine showed carbonyl stretching bands at 1528 cm1 (Figure 2b). Furthermore the IR spectrum of the kneaded budesonide-L-leucine in a ratio of 1:1 (Figure 2a) showed all the carbonyl stretching bands of budesonide and the spray dried L-leucine and indicated that there was no chemical interaction between budesonide and L-leucine when they were kneaded together. Thermal analysis Budesonide was supplied as a micronized powder and the DSC analysis of this powder confirmed the crystalline nature of the starting material as only one endothermic peak at 260 C was observed (Figure 3b) as well as an endothermic
peak of the spray dried L-leucine at 300 C (Figure 3a). Spray dried budesonide was demonstrated to be amorphous (Tajber et al., 2009a; Boraey et al., 2012) and Tajber et al. (2009a) reported that a glass transition (Tg) and a recrystallization exotherm was seen in the thermogram of the spray dried budesonide with a peak at 89.5 C and 130 C, respectively, and this was followed by a melting endotherm with a peak at 262 C (Tajber et al., 2009a). The high glass transition temperatures of these amorphous samples indicated a good physical stability when stored at room temperature (Nolan et al., 2009). Consequently the endothermic peak at 280 C was seen in the thermogram of the co-spray dried budesonideL -leucine in the ratio of 1:50 (Figure 3c) and this may result from the shifted melting point of the spray dried L-leucine alone and the peaks were more diffuse as a result of losing the ordering of the crystal lattice. The exotherm was not seen in the thermogram of the co-spray dried budesonide-L-leucine (a ratio of 1:50) due to the eutectic mixture that may form followed by a glass transition and a recrystallization. A twophase solid-liquid system was formed and it was composed of a liquid phase (budesonide in L-leucine) and a pure solid L -leucine to form a mixed crystal (Martin et al., 1993). This indicated that budesonide was amorphous in the co-spray dried powder which was useful for enhancing its solubility and the dissolution properties of the insoluble drug that would improve their pulmonary absorption. Figure 3(d) shows the thermogram of the kneaded budesonide-L-leucine in a ratio of 1:1. One endothermic peak at 215 C was observed and that may result from the shifted melting point of budesonide. It was noticed that the endothermic peak of L-leucine was not seen in this thermogram due to the formation of a eutectic mixture. Determination of the drug–carrier detachment force Drug adhesion to the carrier can be influenced by the surface of the drug and carrier, the drug to carrier ratio, the carrier
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Table 5. Drug content, coefficient of variation (CV) and in vitro aerosolization properties of the dry powders (mean SD, n 3).
Formulation L1 LM1 LM2 LM3
Content (%)a
CV (%)
ED (%)
FPF (%)
MMAD (mm)
GSD
93.7 1.9 93.0 2.4 92.6 1.8 94.7 1.6
1.99 2.78 2.39 1.81
73.8 2.8 75.6 1.2 77.2 2.4 76.6 1.0
49.4 3.2 67.7 1.0 67.4 1.9 64.3 3.8
2.24 0.11 1.86 0.04 1.94 0.07 2.09 0.10
3.30 0.05 2.93 0.01 2.90 0.03 2.92 0.05
a
n ¼ 5. ED, emitted dose; FPF, fine particle fraction; MMAD, mass median aerodynamic diameter, GSD, geometric standard deviation.
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detachment during aerosolization (Schiavone et al., 2004; Telko & Hickey, 2005). Figure 4. Drug–carrier detachment forces of budesonide dry powder inhalers (Formulations L1, LM1, LM2 and LM3) by ultracentrifugation (mean SD, n ¼ 3).
Table 4. Adhesion force of formulations L1, LM1, LM2 and LM3 at 50% of drug detachment (mean SD, n ¼ 3).
Formulation L1 LM1 LM2 LM3
Adhesion force (mN) At 50% of drug detachment (SD) 5.25 0.10 4.77 0.04 3.98 0.26 3.55 0.28
particle size the mixing time and method, the amount of moisture and the electrostatic behavior (Schiavone et al., 2004; Beilmann et al., 2007). The median g-force was used to approximate the interaction between the co-spray dried powder and the sieved mannitol in the DPI formulations as shown in Figure 4. The drug–carrier detachment profiles changed when we changed the type of a carrier and the drug to carrier ratio. The co-spray dried powder of budesonideL-leucine blended with the sieved mannitol (Formulations LM1 to LM3) had a much lower median g-force than that of the co-spray dried budesonide-L-leucine alone (Formulation L1). Furthermore with formulations of LM1 to LM3 with different ratios of sieved mannitol, the formulation LM3 with the highest ratio of sieved mannitol showed the lowest median g-force compared to the other two formulations. The median adhesion force can be defined as the adhesion force at which there is a 50% probability that the drug particles separate through the sieves after centrifugation. It can be calculated by the regression equation obtained from the log-probability plots of the percentage of drug detachment versus the Xg-force. The calculated results of the median adhesion force of all formulations are shown in Table 4. The results of the median adhesion force correlated with the results of the median g-force, i.e. the formulation blended with the sieved mannitol exhibited a lower median adhesion force than that of the co-spray dried budesonide-L-leucine alone. It was clear that using sieved mannitol as a coarse carrier decreased the adhesion force between the budesonide and the carriers. The adhesion force must be sufficient to avoid demixing during metering but small enough to allow for
In vitro powder aerosolization The in vitro aerosolization and deposition of the DPI formulations has been summarized in Table 5. The ED, FPF and MMAD indicated the effectiveness of the aerosol performance. The percentages of ED for all formulations were not statistically different, in the range of 74–77% of the dose contents released during aerosolization. The MMAD obtained during aerosolization of all formulations were varied between 1.9 and 2.2 mm all of which were suitable for pulmonary drug delivery. The MMAD of the formulations blended with sieved mannitol had a lower MMAD than the co-spray dried formulation, but it was not statistically different when compared with the formulation LM3. In a similar manner, the FPF of the co-spray dried powder of budesonide-L-leucine was statistically (p value 50.05) lower than the FPF of the co-spray dried powder blended with sieved mannitol (Table 5). The co-spray dried powder blended with sieved mannitol showed better aerosolization properties with an FPF in the range of 64–68% while the co-spray dried powder of budesonide-L-leucine had the FPF of 49%. The geometric standard deviation (GSD) or an aerodynamic particle size spread of all DPI formulations was in the range of 2.9–3.3 (Table 5), and thus were polydisperse powders. The co-spray dried powder of budesonide-L-leucine was prone to behave as a high powder aggregation due to interparticulate forces between the fine particles. An uncontrolled powder aggregation led to variations of the sizes of the agglomerates resulting in polydisperse powders. The formulation blended with sieved mannitol exhibited a decrease in the GSD due to the better powder dispersibility. However, after aerosolization the fine particles were separated from the coarse carrier, while some of them were able to aggregate again. Typical GSD values for the aerosol particles were between 1.3 and 3.0 (El-Gendy et al., 2008). In comparison, the co-spray dried powder of budesonide-Lleucine blended with sieved mannitol had a FPF of 64–68% while Nolan et al. (2009) demonstrated that the FPF of the micronized budesonide carried out on the Pulmicort 400 mg TurbuhalerÕ at a flow rate of 58 L/min was 53% with an MMAD of 2.9 mm (Nolan et al., 2009). It was clear that the co-spray dried powder of budesonide-L-leucine blended with sieved mannitol showed better aerosolization than that of the commercial product with a higher FPF and a lower MMAD. Hence the DPI formulation of the co-spray dried
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budesonide-L-leucine blended with the sieved mannitol could potentially lead to a reduction in the prescribed dose of budesonide without reducing therapeutic efficacy. Micronized particles are often highly charged and cohesive, resulting in significant downstream processing and poor product performance (Schiavone et al., 2004). Addition of L-leucine to a dry powder inhaler has been demonstrated to improve the aerosolization properties of the micronized drug by the formation of a crystalline L-leucine shell around the active pharmaceutical ingredient during the evaporation of droplets that resulted in a reduction of the cohesive forces and improved powder dispersion (Boraey et al., 2012). However, using a high amount of L-leucine as the lone carrier by cospray dried with micronized drug, the co-spray dried powders were fine so they exhibited powder cohesion. The blending of mixtures of micronized drug particles that adhered to the surface of the coarse carrier particles has been employed to reduce the cohesion forces between the primary drug particle (Schiavone et al., 2004; Beilmann et al., 2007). Moreover, the blend systems significantly enhanced drug particle flowability, thus improving the dosing accuracy and minimizing the dose variability observed with neat drug formulations and making them easier to handle during the manufacturing operations (Schiavone et al., 2004). Hence the blending of the sieved mannitol as a coarse carrier into the co-spray dried powder of budesonide-L-leucine reduced the interparticulate forces between the micronized powders and consequently, these dry powders behaved as low powder aggregates leading to a high FPF. Furthermore, it was confirmed by the drug–carrier detachment test that for the formulations of LM1 to LM3 and L1, the median adhesion forces of the formulation LM1 to LM were in the range of 3.6–4.8 mN and were lower than that of the formulation L1 (5.3 mN). This indicated that the adhesion force of the co-spray dried powder was reduced when sieved mannitol was added. The drug deposition profile of formulations L1 and LM1 are shown in Figure 5, and both formulations travelled as far as the final stage of the ACI. Although formulation LM1 retained in the device higher than that of formulation L1, the percentage of ED of both were not statistically different. Formulation LM1 demonstrated good dispersibility with a high deposition on stage 2, 3 and 4 of the ACI resulting in a higher FPF than that of formulation L1. While the DPI formulations were aerosolized through the device, the blending of the sieved mannitol with the co-spray dried powder was demonstrated to reduce the cohesive force between the micronized particles with low powder aggregation. Whereas the co-spray dried powder alone significantly deposited higher in the pre-separator which reduced the particle fraction deposited on the impactor stages and resulted in a lower FPF. This could be due to the presence of particle agglomerates. Previous studies have reported that the blending ratio of the carrier can impact aerosol performance. Schiavone et al. (2004) suggested that the excess drug particles could possibly mitigate strong binding carrier–drug and carrier–carrier interactions, thus allowing for more efficient aerosolization (Schiavone et al., 2004). Hamishehkar et al. (2010) demonstrated that the deposition profiles of PLGA microcapsules with higher carrier ratio caused a lower FPF of microcapsules.
Drug Deliv, 2014; 21(6): 397–405
Figure 5. Drug deposition after aerosolization of formulations L1 (white bars) and LM1 (dark bars) into the Andersen cascade impactor at an air flow rate of 60 L/min (mean SD, n ¼ 3).
This result may also be attributed to the ‘‘hot spot theory’’ that indicates that a high drug load in the mix occupies the active sites on the carrier surface and enables the remaining drug particles to adhere at the low energy sites to be more easily detached (Steckel et al., 2004). However, there was no effect of the blending ratio on the FPF (p value40.05) among the formulations LM1 to LM3, although the drug–carrier detachment results showed that an increase of the ratio of the sieved mannitol produced a lower drug–carrier adhesion force (in the same amount of powder load). For in vitro powder aerosolization, all factors were controlled to produce a similar condition, except the amount of the powder load for each formulation. During inhalation, the drug particles were detached from the carrier particle surface by the energy of the inhalation flow. It was possible that using a high amount of the powder load might reduce the shearing force of the airflow that affected the powder aerosolization.
Conclusions Although the co-spray dried powder of budesonide mixed with a high amount of L-leucine, as a carrier, can be prepared with an appropriate aerodynamic size for pulmonary delivery the co-spray dried powder was prone to aggregation due to interparticulate forces between the fine particles that resulted in a reduction of the dispersibility during inhalation. The blending of sieved mannitol, as a coarse carrier, with the cospray dried budesonide-L-leucine had a high FPF, an improved in vitro deposition property compared to the cospray dried powder alone, and that was attributed to improvement of the aerosolization due to the reduced interparticulate forces of the co-spray dried powder. The mass ratio of the sieved mannitol at 20–80 blended with the co-spray dried powder of budesonide-L-leucine (at a ratio of 1:50) provided good aerosolization performance with the FPF of 64–68% that was higher than the FPF of the commercial product (Pulmicort 400 mg TurbuhalerÕ ). It is therefore postulated that those formulations would deliver the majority of the ED to the lower stage of ACI via a passive single-unit dose device with minimal deposition on the pre-separator and stage that would significantly reduce the amount of the drug reaching the bronchi.
DOI: 10.3109/10717544.2013.868555
Acknowledgements The authors would like to thank Dr Brian Hodgson for editing the manuscript.
Declaration of interest This work was supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission, Graduate School, Prince of Songkla University and Nanotec-PSU Excellence Center on Drug Delivery System. The authors report no declaration of interest.
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