http://informahealthcare.com/ddi ISSN: 0363-9045 (print), 1520-5762 (electronic) Drug Dev Ind Pharm, Early Online: 1–8 ! 2015 Informa Healthcare USA, Inc. DOI: 10.3109/03639045.2015.1062512
RESEARCH ARTICLE
Optimizing the dermal accumulation of a tazarotene microemulsion using skin deposition modeling Drug Dev Ind Pharm Downloaded from informahealthcare.com by Yale Dermatologic Surgery on 07/07/15 For personal use only.
Maha Nasr and Sameh Abdel-Hamid Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt
Abstract
Keywords
Context: It is well known that microemulsions are mainly utilized for their transdermal rather than their dermal drug delivery potential due to their low viscosity, and the presence of penetration enhancing surfactants and co-surfactants. Objective: Applying quality by design (QbD) principles, a tazarotene microemulsion formulation for local skin delivery was optimized by creating a control space. Materials and methods: Critical formulation factors (CFF) were oil, surfactant/co-surfactant (SAA/CoS), and water percentages. Critical quality attributes (CQA) were globular size, microemulsion viscosity, tazarotene skin deposition, permeation, and local accumulation efficiency index. Results and discussion: Increasing oil percentage increased globular size, while the opposite occurred regarding SAA/CoS, (p ¼ 0.001). Microemulsion viscosity was reduced by increasing oil and water percentages (p50.05), due to the inherent high viscosity of the utilized SAA/CoS. Drug deposition in the skin was reduced by increasing SAA/CoS due to the increased hydrophilicity and viscosity of the system, but increased by increasing water due to hydration effect (p ¼ 0.009). Models with very good fit were generated, predicting the effect of CFF on globular size, microemulsion viscosity, and drug deposition. A combination of 40% oil and 45% SAA/CoS showed the maximum drug deposition of 75.1%. Clinical skin irritation study showed that the aforementioned formula was safe for topical use. Conclusion: This article suggests that applying QbD tools such as experimental design is an efficient tool for drug product design.
Control space, dermal, drug deposition, microemulsion, quality by design, topical delivery
Introduction The quality by design (QbD) paradigm introduced by ICH Q8 quality guideline provides a thorough understanding of drug products. This could be established through a multidimensional combination and interaction of drug product attributes or what is known as design space1–3. This would result in high level of quality assurance, and facilitate risk based regulatory decisions. Therefore, in this study, we aimed for creating a control space for topical microemulsion formulation through a knowledge-based decision. Microemulsions are isotropic mixtures of oil/water/ surfactants, and co-surfactants with a particle size not exceeding 100 nm in most cases4. As drug carriers, microemulsions are known for their ability to modify the thermodynamic activity of drugs in a way which favors their penetration of the stratum corneum, by virtue of their continuously fluctuating interfaces5,6 and their permeation enhancer components which decrease the diffusional barrier of the stratum corneum7. When topical
Address for correspondence: Sameh Abdel-Hamid, PhD, Faculty of Pharmacy, Department of Pharmaceutics and Industrial Pharmacy, Ain Shams University, Monazamet El Wehda El Afrikia Sreet, El Abbassia, Cairo, Egypt. Tel: +201001056369. Fax: +20224051107. E-mail: [email protected]
History Received 3 January 2015 Revised 29 May 2015 Accepted 10 June 2015 Published online 2 July 2015
delivery is concerned, the main problem which should be overcomed is the poor flux of the drug from the vehicle into the skin where it is required to produce its therapeutic action. Therefore, the drug has to diffuse out of the microemulsion into the skin, penetrate into the skin then diffuse to its target site. The increased thermodynamic activity of the drug towards the skin favors this transport process, driven by passive diffusion which is proportional to the concentration gradient across the skin. However, it is well known that microemulsions are mainly utilized for their transdermal delivery potential owing to their low viscosity, and the presence of penetration enhancing surfactants and co-surfactants. Therefore, instead of preparing microemulsion based gels and hydrogels, in this study, we attempted the manipulation of critical formulation factors (CFFs) in order to accentuate the microemulsion’s topical (dermal) rather than transdermal drug delivery potential. For the microemulsion system, jojoba oil was selected as the tested oil due to its reported excellent skin penetration potential, its wide use in topical preparations, and its desirable antiinflammatory and moisturizing effects essentially required for psoriasis treatment8,9. Moreover, due to its waxy nature, it is expected to decrease the transdermal delivery of drugs10, and enhance topical drug skin deposition instead. As surfactant and co-surfactant, respectively, Tween 80 and span 85 were selected
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due to their reported low irritant and toxic effects5,11,12. Span could also be called a linker which is used to stabilize the microemulsion structure13. In a study by Shevachman et al. and El-Hadidy et al., Tween 80 was able to produce large isotropic microemulsion region with jojoba oil being the oily phase14,15. A model lipophilic drug (tazarotene of a log P ¼ 5.96) was chosen for this study. Tazarotene is a synthetic retinoid used topically in the treatment of psoriasis, since it was reported to normalize the abnormal differentiation of keratinocytes, and reduce their hyperproliferation, with reduction of inflammatory markers while being a troublesome drug formulation-wise owing to its extreme lipophilicity. Therefore, the aim of the current work is to use QbD approach to create a topically oriented microemulsion formulation loaded with tazarotene to be utilized in the treatment of psoriasis.
Materials and methods Materials Tazarotene was kindly gifted by Marcyrl Pharmaceutical Company, Egypt. Jojoba oil was purchased from the Egyptian Natural Oil Company. HPLC grade water and acetonitrile were purchased from Fisher Scientific company, UK. Tween 80, Span 85, acetic acid, potassium dihydrogen phosphate, disodium hydrogen phosphate and sodium chloride were purchased from El-Nasr Pharmaceutical Company, Egypt. Phosphotungistic acid was purchased from Sigma Pharmaceutical Company (Monticello, IA). Methods Pseudoternary phase diagram construction Water dilution titration method was used for the construction of the phase diagram16. For the system, jojoba oil was selected; Tween 80 and span 85 were the surfactant and cosurfactant, respectively. Tween 80 was reported to provide superior solubility for tazarotene17. A constant weight ratio 3:1 of Tween 80 to Span 85 was employed, and the ratios of jojoba oil to the mixture of SAA/CoS were varied as 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 and 9:118. After reaching equilibrium, the prepared mixtures were assessed visually, and under a polarized microscope (Axiostar plus, Zeiss, Germany) to distinguish between microemulsions, crude emulsions, and liquid crystalline phases8. Pseudoternary phase diagrams were constructed using Tri-plot software version 1.4.219. Preparation of tazarotene microemulsions From the constructed pseudoternary phase diagram, selected points were chosen for the preparation of tazarotene microemulsions based on a vertex centroid quadratic design (Table 1).
Table 1. Vertex-centroid quadratic design for preparation of tazarotene loaded microemulsions. Run 1 2 3 4 5 6 7 8a 8b
Oil [%]
SAA/CoS [%]
Water [%]
10 10 15 23 25 40 40 40 40
75 80 80 67 60 45 50 55 55
15 10 5 10 15 15 10 5 5
Tazarotene (0.1% w/w) was dissolved in the designated amount of surfactant/co-surfactant by magnetic stirring, followed by the gradual addition of oil and the drop-wise inclusion of the aqueous phase under magnetic stirring. The concentration of the drug was chosen to mimic the tazarotene concentration in the marketed topical creams or gels. Particle size/zeta potential/conductivity measurement Particle size, zeta potential, and conductivity of the prepared tazarotene microemulsion formulations were measured using Zetasizer (nanoZS, Malvern, Worcestershire, UK)20,21. Viscosity measurement The viscosity of tazarotene microemulsion formulations as well as individual microemulsion components was measured at room temperature at 100 rpm using a viscometer (DVIII, Brookfield, WI) employing spindle number 5215. Transmission electron microscopy In order to examine the microstructure of the prepared microemulsion system, a selected tazarotene loaded microemulsion was placed on a carbon-coated copper grid, and negatively stained with 1% phosphotungistic acid, with the excess stain removed using a filter paper4,7, followed by transmission electron microscopy (TEM) examination (Jeol JEM 1010, Tokyo, Japan). Ex vivo tazarotene skin deposition Mouse skin was carefully cleaned under cold running water, inspected for integrity and stored at 20 C before use. The skin was defrosted, cut into square pieces and clamped with the stratum corneum uppermost in Franz-type diffusion apparatus (model Variomag Telesystem, H + P Labortechnik, Germany). The diffusion area of the cells was 1.77 cm2 and the receptor medium was 7.5 ml phosphate buffer saline (pH 7.4) containing 10% Tween 80, which was constantly stirred at 150 rpm with a small magnetic bar. The receptor compartment was maintained at 37 ± 0.2 C by a circulating water jacket22. A constant volume of the tazarotene microemulsion formulation was placed in the donor compartment. After 24 h, samples were withdrawn from the receptor compartment via the sampling port, and the skin surface was washed five times with distilled water then dried with filter paper to remove any excess drug. The washed skin specimens were placed each in methanol, followed by sonication to extract the deposited drug23. Buffer samples were also withdrawn and diluted with methanol. All samples were filtered with membrane filter of pore size 220 nm before injection into the HPLC column to be analyzed for tazarotene content as described in the previous section. The amount of tazarotene accumulated into the skin was expressed as a percentage of the total drug amount applied on the skin. The local accumulation efficiency index (LAEI) was described using the following equation15. LAEI ¼
Amount of drug deposited in the skin Amount of the permeated drug
High-performance liquid chromatography analysis of tazarotene Quantification of tazarotene in the ex vivo skin deposition study was achieved using a validated high performance liquid chromatography (HPLC) method described by Madhu et al.24 (Agilent, Santa Clara, CA). The mobile phase was a mixture of acetonitrile:water:acetic acid (65:34.5:0.5). The flow rate of mobile phase was 1.2 ml/min and the injection volume was 10 ml. Samples were injected into a C18 column (Agilent Eclipse
DOI: 10.3109/03639045.2015.1062512
XDB, 5 mm, 4.6 250 mm), and the column effluent was monitored at 345 nm. Skin irritation study A skin irritation study was conducted following the approval of the research ethics committee for experimental and clinical studies at the Faculty of Pharmacy, Ain Shams University (approval number REC-ASU 6). A selected tazarotene microemulsion formula was clinically tested on human volunteers, following the application of a certain amount of the formula on the inner arm skin25, and left for 24 h. The treated areas were observed afterwards for any signs of erythema or erosion. The volunteers were instructed to report any signs of irritation occurring after this time period.
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Statistical analysis and modeling of data To study the effect of different formulation variables, runs for microemulsion formulations were generated according to an experimental design using STAVEXÕ 5.1 (Aicos, Switzerland) applying a vertex-centroid design quadratic; D-optimal design. Oil (10–40%), surfactant/co-surfactant (SAA/CoS 45–80%) and water (5–15%) were the critical formulation factors (CFF). Levels of CFF were chosen based on the obtained pseudo-ternary phase diagram and preliminary experiments. Globular size, microemulsion viscosity, drug deposition, permeation and local accumulation efficiency index were the critical quality attributes (CQA). Least square analysis was applied for the fitted model of optimization. The model was evaluated in terms of statistical significance using analysis of variance (ANOVA) at a level of significance p50.05.
Results and discussion Pseudoternary phase diagram The pseudoternary phase diagram prepared using jojoba oil, water and Tween 80/Span 85 mixtures is illustrated in Figure 1. The black shaded area represents the translucent microemulsion region, while the rest either represents turbid phases or liquid crystalline phases observed using the polarizing microscope. No attempt was made to distinguish between o/w, w/o or bicontinuous microemulsion regions4,26. Tween 80 was a well-suited surfactant for our system due to its bulky head group, allowing it to pack more loosely at the interface and to better incorporate oil chains within surfactant tails14. Our system showed a larger
Figure 1. A pseudoternary phase diagram constructed using jojoba oil, tween 80, and span 85 upon titration with water.
Optimizing the dermal accumulation of a microemulsion
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microemulsion region compared to that reported by Shevachman et al.14 which may be attributed to the presence of Span 85 as co-surfactant. Span 85 decreases the HLB of Tween 80 favoring better penetration of jojoba oil into the hydrophobic zone of Tween 80, and hence, formation of microemulsion over a wider range of composition27,28. Characterization of the prepared tazarotene microemulsions Regarding zeta potential, microemulsions displayed a negative charge ranging from 4 to 18, with conductivity ranging from 2 to 12 mS/cm) due to the low percentages of water utilized in the experimental design, suggesting their probable w/o nature6. Upon morphological examination of microemulsion (run number 6), the particles were found to have a spherical shape similar to what was obtained by Patel et al. and Barot et al.29,30 (Figure 2), with their nanometer size confirmed. Upon clinical examination of the same formula, no signs of erythema or skin sensitization were observed and no reports of skin inflammation were received postapplication. This could be attributed to the non-ionic nature of the utilized SAA/CoS in addition to the moisturizing nature of jojoba oil. As evident in Table 2, depending on the different CFFs, microemulsion formulations were found to display a particle size ranging from 6 to 51 nm), viscosity values ranging from 222 to 671 cp and ex vivo skin deposition for tazarotene ranging from 7% to 79%. Statistical analysis and modeling of data Table 2 shows the values of different CQAs for the tazarotene microemulsion according to the runs generated in Table 1. The statistical results were expressed in terms of p values for the investigated CFFs, and their interactions. The fit for the models regarding the CQAs; particle size, viscosity of microemulsion and deposition of tazarotene in the skin was very good as shown in Table 3. By applying the Shapiro–Wilk test, there was no evidence for non-normality of model deviations. Means were
Figure 2. Transmission electron microscopic picture for a negatively stained microemulsion (run number 6) at 120 000.
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Table 2. Results of the runs generated from Vertex-centroid quadratic design showing values for the critical quality attributes: particle size, viscosity, deposition, permeation and local accumulation efficiency index. Run 1 2 3 4 5 6 7 8a 8b
Oil [%]
SAA/CoS [%]
Water [%]
Particle size (nm)
Viscosity (cp)
Deposition [%]
Permeation [%]
LAEI*
10 10 15 23 25 40 40 40 40
75 80 80 67 60 45 50 55 55
15 10 5 10 15 15 10 5 5
13.93 ± 1.15 6.04 ± 1.36 18.77 ± 2.61 20.21 ± 1.09 30.5 ± 0.99 51.3 ± 4.76 38.75 ± 3.3 34.97 ± 8.5 33.42 ± 0.41
574 ± 4.58 598 ± 4.50 671 ± 5.60 520 ± 5.94 460 ± 2.38 222 ± 15.86 331 ± 12.13 381 ± 7.00 373 ± 4.51
33.74 ± 2.99 21.69 ± 1.36 7.64 ± 0.91 29.46 ± 4.17 43.59 ± 2.28 79.25 ± 9.33 37.91 ± 1.76 20.99 ± 6.53 22.37 ± 7.42
3.37 ± 0.71 4.91 ± 1.86 0** 3.03 ± 0.85 3.14 ± 1.38 2.98 ± 0.60 0 0 0
10.01 4.42 0 9.72 13.88 26.59 0 0 0
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The results are represented as mean ± SD (n ¼ 3). *LAEI: Local Accumulation Efficiency Index. **0 means that no tazarotene was detected in the buffer.
Table 3. Fitted models for optimization (least squares) for microemulsion particle size, viscosity and deposition showing the effect of the investigated variables, oil (O), SAA/CoS (S), and water (W) as well as their interactions. Particle size (nm) 2
R ¼ 0.9930 +19.85 +0.6829 O* 0.2829 S* +0.3251 W +5.062e05 O.S +0.002137 O.W 0.05402 S.W* 0.0005383 O2 +0.004022 S2 +0.1785 W2
Viscosity (cp) 2
R ¼ 0.9893 +532.6 5.955 O* +3.426 S* 9.254 W* +0.09839 O.S 0.05297 O.W 0.05237 S.W 0.1318 O2 0.01298 S2 +0.2364 W2
Deposition [%] R2 ¼ 0.9635 +23.99 +0.1700 O 0.5136 S* +3.050 W* 0.01471 O.S +0.04728 O.W 0.03945 S.W +0.01114 O2 +0.005468 S2 +0.07777 W2
R2 is the model goodness of fit. *Significant factor or interaction (p50.05).
Figure 3. Normal plots of model deviations for microemulsion: (a) particle size, (b) viscosity, and (c) deposition.
independent on factor level as evident in Figure 3. On the other hand, permeation and local accumulation efficiency index for the drug showed poor model fitting (models not shown). Effect of the CFF on the globular size of tazarotene microemulsion Both oil and SAA/CoS had a significant effect on microemulsion particle size (p ¼ 0.001). By increasing the oil ratio, particle size
was increased while the opposite occurred regarding SAA/CoS, as evident in Figure 4. Interaction of SAA/CoS and water also reduced the particle size of microemulsions (p ¼ 0.01). Regarding optimization, a combination of 10% oil and 79.5% SAA/CoS showed the minimum particle size of 7.83 nm (Figure 5). The same figure also shows that a combination of 40% oil and 45% SAA/CoS resulted in a maximum particle size of 51.3 nm. Cui et al.31 showed that the percentages of oil, surfactant, and co-surfactant had a significant effect on the particle size of
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DOI: 10.3109/03639045.2015.1062512
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Figure 4. Plot of microemulsion particle size versus (a) oil, and (b) SAA/CoS levels.
SAA/CoS increased the viscosity, as evident in Figure 6. This was due to the high inherent viscosity of SAA/CoS (being 605 and 300 cp for Tween 80 and Span 85, respectively), and low oil viscosity (33 cp). Similar results were obtained by Butani et al28. A combination of 40% oil and 45% S/CoS showed a minimum viscosity of 235.8 cp (Figure 7). This decrease in viscosity was expected to increase the diffusion of the microemulsion system, and hence it would allow easier skin permeation. However, the opposite took place in our case, and it actually led to the highest percentage of tazartoene skin deposition. This could be attributed to the fact that by increasing surfactant mixture, drug diffusion from internal to external phase was reduced due to increased thickness at oil/water interface33. Effect of the CFF on the deposition of tazarotene microemulsion in the skin Figure 5. Contour plot showing the effect of oil, SAA/CoS, and water combination on the particle size of tazarotene microemulsion.
microemulsion formed from SMEDDS, necessitating the optimization of these components. Concurring with our results, other authors reported that increasing the oil component in microemulsion resulted in increased droplet size32. Reduction of particle size by increasing the SAA/CoS % is attributed to surface tension depression, or the reduction of surfactant packing diameter which would result in the increase of the surfactant film mean curvature. This is also in accordance with what was reported by Shevachman et al.14. However, the smaller the particle size, the more is the ability of the microemulsion to result in transdermal penetration rather than local delivery for drugs18. Effect of the CFF on the viscosity of tazarotene microemulsion All three factors had a significant effect on the microemulsion viscosity; oil (p ¼ 0.003), SAA/CoS (p ¼ 0.001) and water (p ¼ 0.01). Both oil and water reduced the viscosity, while
Microemulsions can increase the drugs’ retention in the skin by virtue of their solubilizing power, which allows the partitioning of the dissolved fraction of the drug into the skin, their interaction with skin lipids, in addition to their nanometer size34. Regarding the deposition, only S/CoS and water percentages had a significant effect (p ¼ 0.009), where by increasing water ratio, the deposition of the drug was increased in the skin (Figure 8), while an opposite effect was shown by SAA/CoS (Figure 9). Gupta et al.35 reported that 5-fluorouracil permeation was increased by increasing microemulsion water concentration. This was attributed to the increased hydration and fluidization of lipids in the stratum corneum skin layer with the reduction of corneocytes packing. Similar results were also reported by other authors34,36. On the other hand, despite their lowering of the particle size, increasing of SAA/CoS percentage would lead to lowering stratum corneum hydration and hence reducing the drug permeation flux33. Another explanation for the reduction of drug deposition by increasing the SAA/CoS ratio could be attributed to increasing hydrophilicity over lipophilicity which leads to retention of the drug in the microemulsion, and
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Figure 6. Plot of microemulsion viscosity versus (a) oil, and (b) SAA/CoS levels.
Figure 7. Contour plot showing the effect of oil, SAA/CoS, and water combination on the viscosity of tazarotene microemulsion.
prevent its deposition in the lipophilic skin. Also, increasing SAA/CoS ratio would increase the viscosity of the microemulsion leading to a reduced drug deposition. Some authors attributed increased drug penetration at low SAA/CoS levels to the increase of drug thermodynamic activity29,37,38. They also reported that at high surfactant mixture concentration, the effect of oil on permeation was non-significant. Another explanation that the oil content was not the determining factor for drug deposition could be that tazarotene saturation level was not reached4. A combination of 40% oil and 45% SAA/CoS showed maximum drug deposition of 75.1% (Figure 10). This combination showed a balance between oil and SAA/CoS with reduced amount of water, which would be very suitable for high drug deposition. Usually microemulsion formulations with low oil and high water contents result in increased drug flux39. This combination of oil and SAA/CoS as mentioned above showed also the minimum viscosity (235.8 cp), and maximum particle size (51.3 nm). On the other hand, minimum particle size 7.83 nm
Figure 8. Plot of tazarotene deposition in the skin versus water levels.
from Figure 4 resulted in minimum drug deposition 21.69% as shown in Figure 10. Smaller globules of microemulsion provide bigger surface area of permeation but less retention in the skin. Deposition of a drug in the skin depends also on its partitioning between the microemulsion and the skin40. By applying two-tailed Pearson correlation, we found that deposition showed a negative moderate correlation (r ¼ 0.7136, p ¼ 0.03) against viscosity. Low viscosity would result in high drug diffusion into the skin, consequently leading to increased drug permeation and accumulation41. On the other hand, deposition showed a direct moderate correlation (r ¼ 0.6646) against particle size, however non-significant (p ¼ 0.051). As expected,
DOI: 10.3109/03639045.2015.1062512
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Conclusion We showed in our study through optimization and modeling that the deposition of a highly lipophilic drug tazarotene (log P ¼ 5.96) in the skin is directly dependent on SAA/CoS, and water ratios of the microemulsion. SAA/CoS ratio influenced the degree of lipophilicity of the system, while water ratio increased the skin hydration. On the other hand, oil percentage had only a noticeable effect on the particle size; however, the later was not correlated to the degree of drug deposition in the skin. A control space for the CFF optimized ranges could be suggested as: Oil (37–41%), SAA/CoS (45–57%) and water (2–18%), of which a combination of 40% oil and 45% SAA/CoS showed a maximum drug deposition of 75.1%. This topically oriented microemulsion formulation could be useful in providing site-specific dermal treatment of psoriasis with minimal drug systemic availability, and high skin tolerability, and hence, future clinical studies on psoriatic patients are recommended.
Acknowledgements The authors would like to thank Marcyrl pharmaceutical company, Egypt, for their kind supply of tazarotene.
Declaration of interest Figure 9. Effect of SAA/CoS concentration on tazarotene deposition in the skin.
The authors report no conflicts of interest.
References
Figure 10. Contour plot showing the effect of oil, SAA/CoS, and water combination on the deposition of tazarotene microemulsion in the skin.
deposition showed a very strong positive correlation against local accumulation, p ¼ 0.0005. Permeation percentage ranged from 0% to 5% (Table 2), which together with the deposition results show that tazarotene was successfully deposited in the skin indicating a high efficacy for the microemulsion system for local rather than transdermal tazarotene delivery. Adopting our approach which is the augmentation of the local rather than the transdermal potential of microemulsions, other authors have utilized cationic microemulsions, relying on the interaction with the negative skin surface to enhance their cutaneous retention42. In our current work, we have utilized a modeling approach for the creation of a design space for the CFFs optimized ranges, which could be suggested as follows: Oil (37–41%), SAA/CoS (45–57%) and water (2–18%). The creation of such optimized microemulsion systems based on this design space would permit high solubilization and penetration enhancement for highly lipophilic drugs like tazarotene, leading to the increased bioavailability of the drug in the skin.
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28. Butani D, Yewale C, Misra A. Amphotericin B topical microemulsion: formulation, characterization and evaluation. Colloids Surf B Biointerfaces 2014;116:351–8. 29. Patel MR, Patel RB, Parikh JR, et al. Investigating effect of microemulsion components: in vitro permeation of ketoconazole. Pharm Dev Technol 2011;16:250–8. 30. Barot BS, Parejiya PB, Patel HK, et al. Microemulsion-based gel of terbinafine for the treatment of onychomycosis: optimization of formulation using D-optimal design. AAPS PharmSciTech 2012;13: 184–92. 31. Cui J, Yu B, Zhao Y, et al. Enhancement of oral absorption of curcumin by self-microemulsifying drug delivery systems. Int J Pharm 2009;371:148–55. 32. Chen H, Chang X, Weng T, et al. A study of microemulsion systems for transdermal delivery of triptolide. J Control Release 2004;98: 427–36. 33. Cui Y, Li L, Gu J, et al. Investigation of microemulsion system for transdermal delivery of ligustrazine phosphate. AJPP 2011;5: 1674–81. 34. Ge S, Lin Y, Lu H, et al. Percutaneous delivery of econazole using microemulsion as vehicle: formulation, evaluation and vesicle–skin interaction. Int J Pharm 2014;465:120–31. 35. Gupta RR, Jain SK, Varshney M. AOT water-in-oil microemulsions as a penetration enhancer in transdermal drug delivery of 5-fluorouracil. Colloids Surf B Biointerfaces 2005;41:25–32. 36. Yuan Y, Li SM, Mo FK, Zhong DF. Investigation of microemulsion system for transdermal delivery of meloxicam. Int J Pharm 2006; 321:117–23. 37. Shah VP. Skin penetration enhancers: scientific perspectives. In: Hsieh DS, ed. Drug permeation enhancement: theory and applications. New York: Marcel Dekker;1994:19–24. 38. Rhee YS, Choi JG, Park ES, Chi SC. Transdermal delivery of ketoprofen using microemulsions. Int J Pharm 2001;228:161–70. 39. Sintov AC, Shapiro L. New microemulsion vehicle facilitates percutaneous penetration in vitro and cutaneous drug bioavailability in vivo. J Control Release 2004;95:173–83. 40. Hua L, Weisan P, Jiayu L, Ying Z. Preparation, evaluation, and NMR characterization of vinpocetine microemulsion for transdermal delivery. Drug Dev Ind Pharm 2004;30:657–66. 41. Huang YB, Lin YH, Lu TM, et al. Transdermal delivery of capsaicin derivative sodium-nonivamide acetate using microemulsions as vehicles. Int J Pharm 2008;349:206–11. 42. Pepe D, McCall M, Zheng H, Lopes LB. Protein transduction domain-containing microemulsions as cutaneous delivery systems for an anticancer agent. J Pharm Sci 2013;102:1476–87.
RESEARCH ARTICLE
Optimizing the dermal accumulation of a tazarotene microemulsion using skin deposition modeling Drug Dev Ind Pharm Downloaded from informahealthcare.com by Yale Dermatologic Surgery on 07/07/15 For personal use only.
Maha Nasr and Sameh Abdel-Hamid Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt
Abstract
Keywords
Context: It is well known that microemulsions are mainly utilized for their transdermal rather than their dermal drug delivery potential due to their low viscosity, and the presence of penetration enhancing surfactants and co-surfactants. Objective: Applying quality by design (QbD) principles, a tazarotene microemulsion formulation for local skin delivery was optimized by creating a control space. Materials and methods: Critical formulation factors (CFF) were oil, surfactant/co-surfactant (SAA/CoS), and water percentages. Critical quality attributes (CQA) were globular size, microemulsion viscosity, tazarotene skin deposition, permeation, and local accumulation efficiency index. Results and discussion: Increasing oil percentage increased globular size, while the opposite occurred regarding SAA/CoS, (p ¼ 0.001). Microemulsion viscosity was reduced by increasing oil and water percentages (p50.05), due to the inherent high viscosity of the utilized SAA/CoS. Drug deposition in the skin was reduced by increasing SAA/CoS due to the increased hydrophilicity and viscosity of the system, but increased by increasing water due to hydration effect (p ¼ 0.009). Models with very good fit were generated, predicting the effect of CFF on globular size, microemulsion viscosity, and drug deposition. A combination of 40% oil and 45% SAA/CoS showed the maximum drug deposition of 75.1%. Clinical skin irritation study showed that the aforementioned formula was safe for topical use. Conclusion: This article suggests that applying QbD tools such as experimental design is an efficient tool for drug product design.
Control space, dermal, drug deposition, microemulsion, quality by design, topical delivery
Introduction The quality by design (QbD) paradigm introduced by ICH Q8 quality guideline provides a thorough understanding of drug products. This could be established through a multidimensional combination and interaction of drug product attributes or what is known as design space1–3. This would result in high level of quality assurance, and facilitate risk based regulatory decisions. Therefore, in this study, we aimed for creating a control space for topical microemulsion formulation through a knowledge-based decision. Microemulsions are isotropic mixtures of oil/water/ surfactants, and co-surfactants with a particle size not exceeding 100 nm in most cases4. As drug carriers, microemulsions are known for their ability to modify the thermodynamic activity of drugs in a way which favors their penetration of the stratum corneum, by virtue of their continuously fluctuating interfaces5,6 and their permeation enhancer components which decrease the diffusional barrier of the stratum corneum7. When topical
Address for correspondence: Sameh Abdel-Hamid, PhD, Faculty of Pharmacy, Department of Pharmaceutics and Industrial Pharmacy, Ain Shams University, Monazamet El Wehda El Afrikia Sreet, El Abbassia, Cairo, Egypt. Tel: +201001056369. Fax: +20224051107. E-mail: [email protected]
History Received 3 January 2015 Revised 29 May 2015 Accepted 10 June 2015 Published online 2 July 2015
delivery is concerned, the main problem which should be overcomed is the poor flux of the drug from the vehicle into the skin where it is required to produce its therapeutic action. Therefore, the drug has to diffuse out of the microemulsion into the skin, penetrate into the skin then diffuse to its target site. The increased thermodynamic activity of the drug towards the skin favors this transport process, driven by passive diffusion which is proportional to the concentration gradient across the skin. However, it is well known that microemulsions are mainly utilized for their transdermal delivery potential owing to their low viscosity, and the presence of penetration enhancing surfactants and co-surfactants. Therefore, instead of preparing microemulsion based gels and hydrogels, in this study, we attempted the manipulation of critical formulation factors (CFFs) in order to accentuate the microemulsion’s topical (dermal) rather than transdermal drug delivery potential. For the microemulsion system, jojoba oil was selected as the tested oil due to its reported excellent skin penetration potential, its wide use in topical preparations, and its desirable antiinflammatory and moisturizing effects essentially required for psoriasis treatment8,9. Moreover, due to its waxy nature, it is expected to decrease the transdermal delivery of drugs10, and enhance topical drug skin deposition instead. As surfactant and co-surfactant, respectively, Tween 80 and span 85 were selected
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due to their reported low irritant and toxic effects5,11,12. Span could also be called a linker which is used to stabilize the microemulsion structure13. In a study by Shevachman et al. and El-Hadidy et al., Tween 80 was able to produce large isotropic microemulsion region with jojoba oil being the oily phase14,15. A model lipophilic drug (tazarotene of a log P ¼ 5.96) was chosen for this study. Tazarotene is a synthetic retinoid used topically in the treatment of psoriasis, since it was reported to normalize the abnormal differentiation of keratinocytes, and reduce their hyperproliferation, with reduction of inflammatory markers while being a troublesome drug formulation-wise owing to its extreme lipophilicity. Therefore, the aim of the current work is to use QbD approach to create a topically oriented microemulsion formulation loaded with tazarotene to be utilized in the treatment of psoriasis.
Materials and methods Materials Tazarotene was kindly gifted by Marcyrl Pharmaceutical Company, Egypt. Jojoba oil was purchased from the Egyptian Natural Oil Company. HPLC grade water and acetonitrile were purchased from Fisher Scientific company, UK. Tween 80, Span 85, acetic acid, potassium dihydrogen phosphate, disodium hydrogen phosphate and sodium chloride were purchased from El-Nasr Pharmaceutical Company, Egypt. Phosphotungistic acid was purchased from Sigma Pharmaceutical Company (Monticello, IA). Methods Pseudoternary phase diagram construction Water dilution titration method was used for the construction of the phase diagram16. For the system, jojoba oil was selected; Tween 80 and span 85 were the surfactant and cosurfactant, respectively. Tween 80 was reported to provide superior solubility for tazarotene17. A constant weight ratio 3:1 of Tween 80 to Span 85 was employed, and the ratios of jojoba oil to the mixture of SAA/CoS were varied as 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2 and 9:118. After reaching equilibrium, the prepared mixtures were assessed visually, and under a polarized microscope (Axiostar plus, Zeiss, Germany) to distinguish between microemulsions, crude emulsions, and liquid crystalline phases8. Pseudoternary phase diagrams were constructed using Tri-plot software version 1.4.219. Preparation of tazarotene microemulsions From the constructed pseudoternary phase diagram, selected points were chosen for the preparation of tazarotene microemulsions based on a vertex centroid quadratic design (Table 1).
Table 1. Vertex-centroid quadratic design for preparation of tazarotene loaded microemulsions. Run 1 2 3 4 5 6 7 8a 8b
Oil [%]
SAA/CoS [%]
Water [%]
10 10 15 23 25 40 40 40 40
75 80 80 67 60 45 50 55 55
15 10 5 10 15 15 10 5 5
Tazarotene (0.1% w/w) was dissolved in the designated amount of surfactant/co-surfactant by magnetic stirring, followed by the gradual addition of oil and the drop-wise inclusion of the aqueous phase under magnetic stirring. The concentration of the drug was chosen to mimic the tazarotene concentration in the marketed topical creams or gels. Particle size/zeta potential/conductivity measurement Particle size, zeta potential, and conductivity of the prepared tazarotene microemulsion formulations were measured using Zetasizer (nanoZS, Malvern, Worcestershire, UK)20,21. Viscosity measurement The viscosity of tazarotene microemulsion formulations as well as individual microemulsion components was measured at room temperature at 100 rpm using a viscometer (DVIII, Brookfield, WI) employing spindle number 5215. Transmission electron microscopy In order to examine the microstructure of the prepared microemulsion system, a selected tazarotene loaded microemulsion was placed on a carbon-coated copper grid, and negatively stained with 1% phosphotungistic acid, with the excess stain removed using a filter paper4,7, followed by transmission electron microscopy (TEM) examination (Jeol JEM 1010, Tokyo, Japan). Ex vivo tazarotene skin deposition Mouse skin was carefully cleaned under cold running water, inspected for integrity and stored at 20 C before use. The skin was defrosted, cut into square pieces and clamped with the stratum corneum uppermost in Franz-type diffusion apparatus (model Variomag Telesystem, H + P Labortechnik, Germany). The diffusion area of the cells was 1.77 cm2 and the receptor medium was 7.5 ml phosphate buffer saline (pH 7.4) containing 10% Tween 80, which was constantly stirred at 150 rpm with a small magnetic bar. The receptor compartment was maintained at 37 ± 0.2 C by a circulating water jacket22. A constant volume of the tazarotene microemulsion formulation was placed in the donor compartment. After 24 h, samples were withdrawn from the receptor compartment via the sampling port, and the skin surface was washed five times with distilled water then dried with filter paper to remove any excess drug. The washed skin specimens were placed each in methanol, followed by sonication to extract the deposited drug23. Buffer samples were also withdrawn and diluted with methanol. All samples were filtered with membrane filter of pore size 220 nm before injection into the HPLC column to be analyzed for tazarotene content as described in the previous section. The amount of tazarotene accumulated into the skin was expressed as a percentage of the total drug amount applied on the skin. The local accumulation efficiency index (LAEI) was described using the following equation15. LAEI ¼
Amount of drug deposited in the skin Amount of the permeated drug
High-performance liquid chromatography analysis of tazarotene Quantification of tazarotene in the ex vivo skin deposition study was achieved using a validated high performance liquid chromatography (HPLC) method described by Madhu et al.24 (Agilent, Santa Clara, CA). The mobile phase was a mixture of acetonitrile:water:acetic acid (65:34.5:0.5). The flow rate of mobile phase was 1.2 ml/min and the injection volume was 10 ml. Samples were injected into a C18 column (Agilent Eclipse
DOI: 10.3109/03639045.2015.1062512
XDB, 5 mm, 4.6 250 mm), and the column effluent was monitored at 345 nm. Skin irritation study A skin irritation study was conducted following the approval of the research ethics committee for experimental and clinical studies at the Faculty of Pharmacy, Ain Shams University (approval number REC-ASU 6). A selected tazarotene microemulsion formula was clinically tested on human volunteers, following the application of a certain amount of the formula on the inner arm skin25, and left for 24 h. The treated areas were observed afterwards for any signs of erythema or erosion. The volunteers were instructed to report any signs of irritation occurring after this time period.
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Statistical analysis and modeling of data To study the effect of different formulation variables, runs for microemulsion formulations were generated according to an experimental design using STAVEXÕ 5.1 (Aicos, Switzerland) applying a vertex-centroid design quadratic; D-optimal design. Oil (10–40%), surfactant/co-surfactant (SAA/CoS 45–80%) and water (5–15%) were the critical formulation factors (CFF). Levels of CFF were chosen based on the obtained pseudo-ternary phase diagram and preliminary experiments. Globular size, microemulsion viscosity, drug deposition, permeation and local accumulation efficiency index were the critical quality attributes (CQA). Least square analysis was applied for the fitted model of optimization. The model was evaluated in terms of statistical significance using analysis of variance (ANOVA) at a level of significance p50.05.
Results and discussion Pseudoternary phase diagram The pseudoternary phase diagram prepared using jojoba oil, water and Tween 80/Span 85 mixtures is illustrated in Figure 1. The black shaded area represents the translucent microemulsion region, while the rest either represents turbid phases or liquid crystalline phases observed using the polarizing microscope. No attempt was made to distinguish between o/w, w/o or bicontinuous microemulsion regions4,26. Tween 80 was a well-suited surfactant for our system due to its bulky head group, allowing it to pack more loosely at the interface and to better incorporate oil chains within surfactant tails14. Our system showed a larger
Figure 1. A pseudoternary phase diagram constructed using jojoba oil, tween 80, and span 85 upon titration with water.
Optimizing the dermal accumulation of a microemulsion
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microemulsion region compared to that reported by Shevachman et al.14 which may be attributed to the presence of Span 85 as co-surfactant. Span 85 decreases the HLB of Tween 80 favoring better penetration of jojoba oil into the hydrophobic zone of Tween 80, and hence, formation of microemulsion over a wider range of composition27,28. Characterization of the prepared tazarotene microemulsions Regarding zeta potential, microemulsions displayed a negative charge ranging from 4 to 18, with conductivity ranging from 2 to 12 mS/cm) due to the low percentages of water utilized in the experimental design, suggesting their probable w/o nature6. Upon morphological examination of microemulsion (run number 6), the particles were found to have a spherical shape similar to what was obtained by Patel et al. and Barot et al.29,30 (Figure 2), with their nanometer size confirmed. Upon clinical examination of the same formula, no signs of erythema or skin sensitization were observed and no reports of skin inflammation were received postapplication. This could be attributed to the non-ionic nature of the utilized SAA/CoS in addition to the moisturizing nature of jojoba oil. As evident in Table 2, depending on the different CFFs, microemulsion formulations were found to display a particle size ranging from 6 to 51 nm), viscosity values ranging from 222 to 671 cp and ex vivo skin deposition for tazarotene ranging from 7% to 79%. Statistical analysis and modeling of data Table 2 shows the values of different CQAs for the tazarotene microemulsion according to the runs generated in Table 1. The statistical results were expressed in terms of p values for the investigated CFFs, and their interactions. The fit for the models regarding the CQAs; particle size, viscosity of microemulsion and deposition of tazarotene in the skin was very good as shown in Table 3. By applying the Shapiro–Wilk test, there was no evidence for non-normality of model deviations. Means were
Figure 2. Transmission electron microscopic picture for a negatively stained microemulsion (run number 6) at 120 000.
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Table 2. Results of the runs generated from Vertex-centroid quadratic design showing values for the critical quality attributes: particle size, viscosity, deposition, permeation and local accumulation efficiency index. Run 1 2 3 4 5 6 7 8a 8b
Oil [%]
SAA/CoS [%]
Water [%]
Particle size (nm)
Viscosity (cp)
Deposition [%]
Permeation [%]
LAEI*
10 10 15 23 25 40 40 40 40
75 80 80 67 60 45 50 55 55
15 10 5 10 15 15 10 5 5
13.93 ± 1.15 6.04 ± 1.36 18.77 ± 2.61 20.21 ± 1.09 30.5 ± 0.99 51.3 ± 4.76 38.75 ± 3.3 34.97 ± 8.5 33.42 ± 0.41
574 ± 4.58 598 ± 4.50 671 ± 5.60 520 ± 5.94 460 ± 2.38 222 ± 15.86 331 ± 12.13 381 ± 7.00 373 ± 4.51
33.74 ± 2.99 21.69 ± 1.36 7.64 ± 0.91 29.46 ± 4.17 43.59 ± 2.28 79.25 ± 9.33 37.91 ± 1.76 20.99 ± 6.53 22.37 ± 7.42
3.37 ± 0.71 4.91 ± 1.86 0** 3.03 ± 0.85 3.14 ± 1.38 2.98 ± 0.60 0 0 0
10.01 4.42 0 9.72 13.88 26.59 0 0 0
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The results are represented as mean ± SD (n ¼ 3). *LAEI: Local Accumulation Efficiency Index. **0 means that no tazarotene was detected in the buffer.
Table 3. Fitted models for optimization (least squares) for microemulsion particle size, viscosity and deposition showing the effect of the investigated variables, oil (O), SAA/CoS (S), and water (W) as well as their interactions. Particle size (nm) 2
R ¼ 0.9930 +19.85 +0.6829 O* 0.2829 S* +0.3251 W +5.062e05 O.S +0.002137 O.W 0.05402 S.W* 0.0005383 O2 +0.004022 S2 +0.1785 W2
Viscosity (cp) 2
R ¼ 0.9893 +532.6 5.955 O* +3.426 S* 9.254 W* +0.09839 O.S 0.05297 O.W 0.05237 S.W 0.1318 O2 0.01298 S2 +0.2364 W2
Deposition [%] R2 ¼ 0.9635 +23.99 +0.1700 O 0.5136 S* +3.050 W* 0.01471 O.S +0.04728 O.W 0.03945 S.W +0.01114 O2 +0.005468 S2 +0.07777 W2
R2 is the model goodness of fit. *Significant factor or interaction (p50.05).
Figure 3. Normal plots of model deviations for microemulsion: (a) particle size, (b) viscosity, and (c) deposition.
independent on factor level as evident in Figure 3. On the other hand, permeation and local accumulation efficiency index for the drug showed poor model fitting (models not shown). Effect of the CFF on the globular size of tazarotene microemulsion Both oil and SAA/CoS had a significant effect on microemulsion particle size (p ¼ 0.001). By increasing the oil ratio, particle size
was increased while the opposite occurred regarding SAA/CoS, as evident in Figure 4. Interaction of SAA/CoS and water also reduced the particle size of microemulsions (p ¼ 0.01). Regarding optimization, a combination of 10% oil and 79.5% SAA/CoS showed the minimum particle size of 7.83 nm (Figure 5). The same figure also shows that a combination of 40% oil and 45% SAA/CoS resulted in a maximum particle size of 51.3 nm. Cui et al.31 showed that the percentages of oil, surfactant, and co-surfactant had a significant effect on the particle size of
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DOI: 10.3109/03639045.2015.1062512
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Figure 4. Plot of microemulsion particle size versus (a) oil, and (b) SAA/CoS levels.
SAA/CoS increased the viscosity, as evident in Figure 6. This was due to the high inherent viscosity of SAA/CoS (being 605 and 300 cp for Tween 80 and Span 85, respectively), and low oil viscosity (33 cp). Similar results were obtained by Butani et al28. A combination of 40% oil and 45% S/CoS showed a minimum viscosity of 235.8 cp (Figure 7). This decrease in viscosity was expected to increase the diffusion of the microemulsion system, and hence it would allow easier skin permeation. However, the opposite took place in our case, and it actually led to the highest percentage of tazartoene skin deposition. This could be attributed to the fact that by increasing surfactant mixture, drug diffusion from internal to external phase was reduced due to increased thickness at oil/water interface33. Effect of the CFF on the deposition of tazarotene microemulsion in the skin Figure 5. Contour plot showing the effect of oil, SAA/CoS, and water combination on the particle size of tazarotene microemulsion.
microemulsion formed from SMEDDS, necessitating the optimization of these components. Concurring with our results, other authors reported that increasing the oil component in microemulsion resulted in increased droplet size32. Reduction of particle size by increasing the SAA/CoS % is attributed to surface tension depression, or the reduction of surfactant packing diameter which would result in the increase of the surfactant film mean curvature. This is also in accordance with what was reported by Shevachman et al.14. However, the smaller the particle size, the more is the ability of the microemulsion to result in transdermal penetration rather than local delivery for drugs18. Effect of the CFF on the viscosity of tazarotene microemulsion All three factors had a significant effect on the microemulsion viscosity; oil (p ¼ 0.003), SAA/CoS (p ¼ 0.001) and water (p ¼ 0.01). Both oil and water reduced the viscosity, while
Microemulsions can increase the drugs’ retention in the skin by virtue of their solubilizing power, which allows the partitioning of the dissolved fraction of the drug into the skin, their interaction with skin lipids, in addition to their nanometer size34. Regarding the deposition, only S/CoS and water percentages had a significant effect (p ¼ 0.009), where by increasing water ratio, the deposition of the drug was increased in the skin (Figure 8), while an opposite effect was shown by SAA/CoS (Figure 9). Gupta et al.35 reported that 5-fluorouracil permeation was increased by increasing microemulsion water concentration. This was attributed to the increased hydration and fluidization of lipids in the stratum corneum skin layer with the reduction of corneocytes packing. Similar results were also reported by other authors34,36. On the other hand, despite their lowering of the particle size, increasing of SAA/CoS percentage would lead to lowering stratum corneum hydration and hence reducing the drug permeation flux33. Another explanation for the reduction of drug deposition by increasing the SAA/CoS ratio could be attributed to increasing hydrophilicity over lipophilicity which leads to retention of the drug in the microemulsion, and
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Figure 6. Plot of microemulsion viscosity versus (a) oil, and (b) SAA/CoS levels.
Figure 7. Contour plot showing the effect of oil, SAA/CoS, and water combination on the viscosity of tazarotene microemulsion.
prevent its deposition in the lipophilic skin. Also, increasing SAA/CoS ratio would increase the viscosity of the microemulsion leading to a reduced drug deposition. Some authors attributed increased drug penetration at low SAA/CoS levels to the increase of drug thermodynamic activity29,37,38. They also reported that at high surfactant mixture concentration, the effect of oil on permeation was non-significant. Another explanation that the oil content was not the determining factor for drug deposition could be that tazarotene saturation level was not reached4. A combination of 40% oil and 45% SAA/CoS showed maximum drug deposition of 75.1% (Figure 10). This combination showed a balance between oil and SAA/CoS with reduced amount of water, which would be very suitable for high drug deposition. Usually microemulsion formulations with low oil and high water contents result in increased drug flux39. This combination of oil and SAA/CoS as mentioned above showed also the minimum viscosity (235.8 cp), and maximum particle size (51.3 nm). On the other hand, minimum particle size 7.83 nm
Figure 8. Plot of tazarotene deposition in the skin versus water levels.
from Figure 4 resulted in minimum drug deposition 21.69% as shown in Figure 10. Smaller globules of microemulsion provide bigger surface area of permeation but less retention in the skin. Deposition of a drug in the skin depends also on its partitioning between the microemulsion and the skin40. By applying two-tailed Pearson correlation, we found that deposition showed a negative moderate correlation (r ¼ 0.7136, p ¼ 0.03) against viscosity. Low viscosity would result in high drug diffusion into the skin, consequently leading to increased drug permeation and accumulation41. On the other hand, deposition showed a direct moderate correlation (r ¼ 0.6646) against particle size, however non-significant (p ¼ 0.051). As expected,
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Conclusion We showed in our study through optimization and modeling that the deposition of a highly lipophilic drug tazarotene (log P ¼ 5.96) in the skin is directly dependent on SAA/CoS, and water ratios of the microemulsion. SAA/CoS ratio influenced the degree of lipophilicity of the system, while water ratio increased the skin hydration. On the other hand, oil percentage had only a noticeable effect on the particle size; however, the later was not correlated to the degree of drug deposition in the skin. A control space for the CFF optimized ranges could be suggested as: Oil (37–41%), SAA/CoS (45–57%) and water (2–18%), of which a combination of 40% oil and 45% SAA/CoS showed a maximum drug deposition of 75.1%. This topically oriented microemulsion formulation could be useful in providing site-specific dermal treatment of psoriasis with minimal drug systemic availability, and high skin tolerability, and hence, future clinical studies on psoriatic patients are recommended.
Acknowledgements The authors would like to thank Marcyrl pharmaceutical company, Egypt, for their kind supply of tazarotene.
Declaration of interest Figure 9. Effect of SAA/CoS concentration on tazarotene deposition in the skin.
The authors report no conflicts of interest.
References
Figure 10. Contour plot showing the effect of oil, SAA/CoS, and water combination on the deposition of tazarotene microemulsion in the skin.
deposition showed a very strong positive correlation against local accumulation, p ¼ 0.0005. Permeation percentage ranged from 0% to 5% (Table 2), which together with the deposition results show that tazarotene was successfully deposited in the skin indicating a high efficacy for the microemulsion system for local rather than transdermal tazarotene delivery. Adopting our approach which is the augmentation of the local rather than the transdermal potential of microemulsions, other authors have utilized cationic microemulsions, relying on the interaction with the negative skin surface to enhance their cutaneous retention42. In our current work, we have utilized a modeling approach for the creation of a design space for the CFFs optimized ranges, which could be suggested as follows: Oil (37–41%), SAA/CoS (45–57%) and water (2–18%). The creation of such optimized microemulsion systems based on this design space would permit high solubilization and penetration enhancement for highly lipophilic drugs like tazarotene, leading to the increased bioavailability of the drug in the skin.
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