Journal of Chromatography B, 947–948 (2014) 96–102

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Determination of lomerizine in human plasma by liquid chromatography/tandem mass spectrometry and its application to a pharmacokinetic study Yulong Ren a,b , Tianshun Liu b , Guoxin Song b , Yaoming Hu b,∗∗ , Jianying Liang a,∗ a b

Department of Pharmaceutical Analysis, School of Pharmacy, Fudan University, 826 Zhangheng Road, Shanghai 201203, PR China Center of Analysis and Measurement, Fudan University, 220 Handan Road, Shanghai 200433, PR China

a r t i c l e

i n f o

Article history: Received 15 October 2013 Received in revised form 17 December 2013 Accepted 19 December 2013 Available online 26 December 2013 Keywords: Lomerizine LC–MS/MS Pharmacokinetics

a b s t r a c t A rapid, sensitive and selective high performance liquid chromatography–electrospray ionization– tandem mass spectrometry method (HPLC–ESI–MS/MS) was developed and validated for the determination and pharmacokinetic investigation of lomerizine in human plasma. Protein precipitation process was used to extract lomerizine from human plasma. Plasma samples were separated by HPLC on an Agela Venusil XBP Phenyl column (100 mm × 2.1 mm, 5 ␮m) using a mobile phase consisting of methanol-2 mM ammonium acetate-formic acid (70:30:0.1, v/v/v) and the flow rate was set at 0.35 mL/min. The total run time was 4.0 min and the elution of lomerizine was at 1.9 min. The detection was performed on a triple quadrupole tandem mass spectrometer in the multiple reaction-monitoring (MRM) mode using the respective [M + H]+ ions m/z 469.2 → 181.0 for lomerizine and m/z 405.2 → 202.9 for the I.S. The calibration curve was linear over the range of 0.1–25 ng/mL (r2 > 0.99) with a limit of quantitation (LOQ) of 0.1 ng/mL. The intra- and inter-day precision (relative standard deviation, RSD) values were below 9.65% and the mean accuracy was from 99.00 to 103.00% at four quality control levels. Lomerizine was stable during stability studies, i.e., long term, auto-sampler and freeze/thaw cycles. The method was successfully applied for the evaluation of pharmacokinetics of lomerizine after single oral doses of 10 mg lomerizine to 18 healthy volunteers. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Migraine, an episodic headache, affects more than 10% of the general population [1]. According to the widely accepted ‘vascular theory of migraine’, the symptoms of migraine are caused by transient ischaemia that induced by vasoconstriction. Since 1980s, vasodilator agents such as flunarizine, verapamil, and nifedipine have been developed as the most popular prophylactic drugs for migraines. However, the common side effects of these agents include hypotension, palpitation, and reflex tachycardia, which are all caused by dilating the peripheral vascular while functioned as vasodilators. Lomerizine, possessing much higher selectivity on cerebral circulation than any other vasodilators, becomes the first-line prophylactic drug for migraine [2–4]. Because concentration of lomerizine in plasma has significant association with efficacy and the plasma protein binding rate of lomerizine is high

∗ Corresponding author. Tel.: +86 21 51980056. ∗∗ Corresponding author. Tel.: +86 21 65643012. E-mail addresses: [email protected] (Y. Hu), [email protected] (J. Liang). 1570-0232/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jchromb.2013.12.026

(approximately 80%) [5], the analysis of lomerizine in plasma is of great clinical importance. The extremely high activity of lomerizine makes it effective even at a very low concentration (nmol/L) [4]. In order to perform pharmacokinetics studies at such a low level of concentration, there is a need for analytical methods that quantify lomerizine in plasma sensitively. So far, the only reported approach to determine lomerizine in plasma was by RP-HPLC-UV [6]. The lower limit of quantitation (LLOQ) of this method was 5 ng/mL (S/N = 3), which could not properly evaluate the elimination phase in human pharmacokinetic study. In addition, for the improvement of sensitivity, complicated and time-consuming sample extraction procedures were used in this method. To date, no other methods are available for the determination of lomerizine and even fewer experiments based on healthy volunteers for pharmacokinetic study have been performed. Simpler and more sensitive assay methods are required to measure lomerizine in human plasma samples. It is well known that the use of mass spectrometry interfaced with HPLC helps to improve the selectivity and sensitivity compared with traditional HPLC–UV method [7–14]. The current study describes a sensitive and simple HPLC–MS/MS method and its application to a clinical pharmacokinetic study of lomerizine tablet in healthy volunteers.

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2. Materials and methods 2.1. Chemicals and reagents Lomerizine standard (99.8% purity with HPLC) was supplied by Shenzhen Wanji Pharmaceutical Ltd. (Shenzhen, China). Flunarizine, used as internal standard (I.S.), was obtained from National Institute for the Control of Pharmaceutical and Biological Products (Beijing, China). HPLC-grade methanol, ammonium acetate, and formic acid were purchased from Shanghai Chemical Reagent Company (Shanghai, PR China). Other chemicals were of analytical reagent grade and purchased from commercial sources. Double distilled water was purified by Millipore SimplicityTM (Millipore, Bedford, MA, USA). The drug-free human heparinized plasma was obtained from Shanghai Blood Center (Shanghai, PR China). 2.2. Instrument An Agilent 1100 system consisting of a G1312A quaternary pump, a G1379A vacuum degasser, a G1316A thermostated column oven (Agilent, Waldbronn, Germany) and a HTS PAL autosampler (CTC Analytics, Switzerland) was used. Mass spectrometric detection was performed on an API 3000 triple quadrupole instrument (Applied Biosystems, Toronto, Canada) in multiple reaction monitoring (MRM) mode. A TurboIonSpray ionization (ESI) interface in positive ionization mode was used. Data processing was performed with Analyst 1.4.1 software package (Applied Biosystems). 2.3. Chromatographic conditions The chromatographic separation was achieved on an Agela Venusil XBP Phenyl column (100 mm × 2.1 mm, 5 ␮m). A mixture of methanol-2 mM ammonium acetate-formic acid (70:30:0.1, v/v/v) was used as mobile phase at a flow rate of 0.35 mL/min. The temperature of column and autosampler were maintained at 40 and 20 ◦ C respectively. The chromatographic run time of each sample was 4.0 min. 2.4. Mass spectrometric conditions The mass spectrometer was operated using ESI source in the positive ion detection. Quantitation was done using multiple reaction monitoring (MRM) mode to monitor the transition of the m/z 469.2 protonated precursor ion to the m/z 181.0 product ion for lomerizine and m/z 405.2 protonated precursor ion to the m/z 202.9 product ion for I.S. (Fig. 1). All the parameters of LC and MS were controlled by Analyst software version 1.4.1. Turbo spray voltage was set at 5000 V. Source temperature was maintained at 500 ◦ C. Nitrogen was used as nebulizing gas (10 L/min) and curtain gas (8 L/min). For collision activated dissociation (CAD), nitrogen was employed as the collision gas at a flow rate of 4 L/min. The compound dependent parameters like collision energy (CE), declustering potential (DP), entrance potential (EP), focusing potential (FP) and collision exit potential (CXP) were optimized at 27 eV, 46, 10, 220, and 15 V for lomerizine and 23 eV, 50, 10, 250, and 15 V for I.S. respectively. Quadrupole 1 and quadrupole 3 were maintained at unit resolution with a dwell time of 200 ms for all the analytes. 2.5. Preparation of stock solutions, calibration standards (CS), and quality control (QC) samples The standard stock solutions of 1.00 mg/mL for lomerizine and 1.00 mg/mL for flunarizine were prepared by dissolving requisite amounts of lomerizine and flunarizine in methanol, respectively.

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The standard stock solutions of lomerizine and flunarizine were further diluted with methanol-water (50:50, v/v) to yield working solutions at several concentration levels. Flunarizine working solution of 10 ng/mL was prepared by diluting the stock solution of 1.00 mg/mL in methanol. This solution was used as the internal standard solution. All the standard stock, intermediate stock, and working stock solutions were prepared and stored at 4 ◦ C until use. Drug-free plasma, i.e., control (blank) plasma, was withdrawn from the deep freezer and allowed to thaw completely before use. The calibration standards (CS) and quality control (QC) samples (QC-LLOQ, quality control at the concentration of lower limit of quantification; QC-LOW, low quality control; QCMED, medium quality control; QC-HIGH, high quality control) were prepared by spiking 190 ␮L of blank plasma with 10 ␮L of working solution of lomerizine (5% of total volume of plasma). Calibration standards were made at 0.1, 0.2, 0.5, 1, 5, 10, and 25 ng/mL for lomerizine. Quality controls were similarly prepared at 0.1 ng/mL (QC-LLOQ), 0.2 ng/mL (QC-LOW), 12 ng/mL (QC-MED), and 20 ng/mL (QC-HIGH) for lomerizine. The spiked plasma samples at all levels were stored at −20 ◦ C until analysis. 2.6. Sample preparation The samples were stored in the freezer at −20 ◦ C and allowed to thaw at room temperature before processing. One hundred microliters of plasma were pipetted to a 2.0 mL of polypropylene tube and 0.5 mL of methanolic with I.S. working solution (flunarizine, 10 ng/mL) was added to precipitate the proteins. The contents were vortex mixed for 1 min. After centrifugation at 15,000 × g for 5 min, a 200 ␮L aliquot of clear supernatant was transferred to the autosampler. A volume of 10 ␮L was injected into the LC–MS/MS system.

2.7. Method validation 2.7.1. Specificity The specificity of the methods was determined by analyzing eight different lots of blank control matrix for the presence of potential interferences in the retention window of the peaks of interest. The influence of the presence of interferences in blank control matrix with and without internal standard was determined by comparing the peak areas with blank control matrix containing the analyte at lower limit of quantitation (LLOQ) level. The acceptance criterion for the ratio between the peak area of interference and the analyte at LLOQ level was 0.2. For interference in the retention window of the internal standard, a criterion of 0.05 was considered acceptable.

2.7.2. Linearity The linearity of the method was determined by the analysis of five calibration curves containing seven non-zero concentrations. The ratio of area response for lomerizine to I.S. was used for regression analysis. Calibration curve was prepared by determining the best fit of peak area ratios (peak area analyte/peak area I.S.) versus concentration, and fitted to the y = bx + c using weighing factor (1/x). Back calculations were made from these curves to determine the concentration of lomerizine in each calibration standard. The correlation coefficient (r) > 0.99 was expected for all the calibration curves. The lowest standard on the calibration curve was to be accepted as the LLOQ, if the analyte response was at least 10 times more than that of drug free (blank) extracted plasma. In addition, the analyte peak of LLOQ sample should be identifiable, discrete, and reproducible with a precision (%RSD) not greater than 20.0 and accuracy within 80.0–120.0%. The accuracy of standards other

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Fig. 1. Product ion spectra of (A) Lomerizine (469.2 → 181.0), (B) I.S. (405.2 → 202.9).

than LLOQ from the nominal concentration should not be more than ±15.0%. 2.7.3. Carry-over effect Carry-over for lomerizine was assessed by injection of blank samples directly after injection of the highest point in the calibration curve. Carry over in the blank sample following the high concentration standard should not be greater than 20% of the LLOQ and 5% for the internal standard. 2.7.4. Intra- and inter-day precision and accuracy For determining the intra-day precision and accuracy, replicate analysis of plasma samples of lomerizine was performed on the same day. The run consisted of a calibration curve and six replicates of QC-LLOQ, QC-LOW, QC-MED, and QC-HIGH samples. The inter-day precision and accuracy were assessed by analysis of six precision and accuracy batches on six consecutive validation days. The precision of the method was determined by calculating the relative standard deviation (%RSD) for each level. The deviation at each concentration level from the nominal concentration was expected to be within ±15.0% except LLOQ for which it should not be more than 20%. Similarly, the mean accuracy should not deviate by ±15.0% except for the LLOQ where it can be ±20% of the nominal concentration. accuracy calculated and expressed in terms of accuracy =  The overall mean detected concentration × 100%. theoretical concentration 2.7.5. Extraction recovery The extraction recoveries of lomerizine at 0.1 ng/mL, 1 ng/mL and 25 ng/mL levels were measured by comparing the peak area of lomerizine in plasma standards to those in the spiked after-protein precipitation blank plasma extracts at the corresponding concentrations (n = 6). Extraction ⎛ ⎞ recovery =

⎜ ⎟ Peak area of analyte from the spiked plasma sample ⎝ Peak area of analyte from the spiked after protein precipitation ⎠ 100%. blank plasma extract sample

2.7.6. Matrix effect The matrix effect was evaluated at three concentrations (0.1, 1, and 25 ng/mL) in plasma. Two groups of samples were prepared: group 1 was prepared to evaluate the MS/MS response for a pure standard of lomerizine dissolved in the mobile phase (A); group 2 was prepared in plasma originating from six different donors and

submitted to the sample purification process and spiked with lomerizine after processing (B). The value (B/A × 100%) was considered as an absolute matrix effect. The inter-subject variability of matrix effect at every concentration level should be less than 15%. 2.7.7. Dilution integrity The dilution integrity experiment was performed with an aim to validate the dilution test to be carried out on higher analyte concentrations (above ULOQ, upper limit of quantification), which may be encountered during real samples analysis. Dilution integrity experiment was carried out at 10 times the ULOQ concentration i.e., 250 ng/mL for lomerizine and also at ULOQ level. Six replicate samples each of 1/10 of 10 × ULOQ (250/25 ng/mL) concentration were prepared and their concentrations were calculated, by applying the dilution factor of 10 against the freshly prepared calibration curve for lomerizine. 2.7.8. Stability The stability in biological matrix was examined by keeping replicates of spiked plasma samples at concentrations of 0.1, 1, and 25 ng/mL at room temperature for 24 h. Freeze–thaw cycles stability of the samples were obtained over three freeze–thaw cycles, by thawing at room temperature for 1–2 h and refrozen (−20 ◦ C) for 12–24 h. Auto-sampler stability of the analytes were tested by storing samples in the auto-sampler tray (20 ◦ C) for 24 h. Longterm stability was tested after storage of analytes for 45 days at −20 ◦ C. For each concentration and storage condition, three replicates were analyzed in one analytical batch with freshly prepared calibration samples. The concentrations of analytes after each storage period were compared to the nominal concentrations of the samples. The samples were considered stable if the deviation from the mean calculated concentration of freshly thawed samples was within ±15.0%. 2.8. Pharmacokinetic study A pharmacokinetic study was performed in healthy Chinese volunteers approved by the Ethical Committee of Zhongshan Hospital, Shanghai, China and performed in accordance with good clinical practice (GCP) norms. 18 healthy adult male Chinese volunteers were eligible based on the following criteria: age 18–30 years and body mass index between 20 and 24 kg/m2 ; no smoking status and no history or evidence of a renal, gastrointestinal, hepatic, or hematologic, or

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any acute or chronic disease, or any allergy to any drugs; no history of using any kind of drugs within 30 days. All volunteers were oral administrated with single oral doses of 10 mg of lomerizine and with 200 mL of water after fasting for 12 h, respectively. 2.0 mL blood was drawn before drug administration (for baseline measurements) and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 12, 15, 24 h after dosing. The blood samples were drawn into a vacuum tube with heparin sodium as an anticoagulant and immediately centrifuged at 2100 × g for 10 min. The separated plasma was transferred into another clean, dry tube and stored at −20 ◦ C until quantitative analysis for the determination of lomerizine in plasma was performed. The plasma concentrations of these blood samples were determined using the LC–MS/MS method, and the main pharmacokinetic parameters of lomerizine were calculated by noncompartmental analysis using the DAS 2.0 (issued by the State Food and Drug Administration of China for Pharmacokinetic Study). The peak plasma concentration (Cmax ) and the corresponding time (tmax ) were directly obtained from the raw data. The area under the curve to the last measurable concentration (AUC0–t ) was calculated by the linear trapezoidal method. The terminal elimination rate constant (ke ) was estimated by linear least-squares regression of the terminal portion of the plasma concentration time curve, and the corresponding elimination half-life (t1/2 ) was then calculated as 0.693/ke . The area under the curve extrapolated to infinity (AUC0–∞ ) was calculated as AUC0–t + Cn /ke , while Cn is the concentration at the last sampling time. 2.9. Incurred sample reanalysis An incurred sample reanalysis (ISR) was also conducted by selection of 36 subject samples near Cmax and the elimination phase. The results obtained were compared with the data obtained earlier for the same sample using the same procedure. The concentration obtained for the initial analysis and the concentration obtained by reanalysis should be within 20% of their mean for at least 67% of the repeats [15]. Change (%) =



Repeat value − initial value Mean of repeat and initial values



× 100

3. Results and discussion 3.1. Method development 3.1.1. Chromatography The chromatographic conditions were optimized to obtain high sensitivity, good peak shape and short retention. The separation and ionization of lomerizine and I.S. were affected by the composition of mobile phase. Methanol and acetonitrile were tested as an organic modifier of mobile phase. Methanol was finally adopted for it produced symmetric peak shape and higher detection response of analyte than acetonitrile. Then, the organic solvent percentage in the mobile phase was investigated over the range of 65–80% and 70% was chosen due to the high response of lomerizine and suitable retention times provided. Formic acid and ammonium acetate were considered as additives in the mobile phase to improve the response of analyte. The concentration of formic acid and ammonium acetate was also investigated. The ionization of lomerizine and I.S. was increased by adding formic acid in the mobile phase. The effect of formic acid of 0.1, 0.2, and 0.5% in aqueous phase on the response was investigated. Both lomerizine and I.S. were found to have higher response in the mobile phase with 0.1% formic acid. More test results showed that better peak shapes and higher response could be achieved by adding 2 mM of ammonium acetate into the aqueous portion. According to

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this, a mobile phase consisting of methanol-2 mM ammonium acetate-formic acid (70:30:0.1, v/v/v) was selected in the method. Even if the analyte and I.S. can be separately detected, the choice of the analytical column is still important. Various columns (Agilent Zorbax SB-C18 column, 100 mm × 3.0 mm, 3 ␮m, Agilent Zorbax Eclipse XDB-C18 column, 150 mm × 2.1 mm, 5 ␮m, or Waters symmetry C8 column, 50 mm × 2.1 mm, 5 ␮m, Gemini C18 column, 100 mm × 2.0 mm, 3 ␮m, and Agela Venusil XBP Phenyl column, 100 mm × 2.1 mm, 5 ␮m) were all tested during the method development. Comparing to other categories of column, phenyl column provides much higher retention due to the similar molecular structure with the analyte and I.S. which is the precondition for the improvement of proportion of organic phase, benefiting ionization and sensitivity. Column temperature (30, 40, 45, or 50 ◦ C), and flow rate of the mobile phase (0.20, 0.30, 0.35, or 0.40 mL/min) were examined and compared. Finally, plasma samples were separated by HPLC on an Agela Venusil XBP Phenyl column (100 mm × 2.1 mm, 5 ␮m) using a solvent system consisting of methanol-2 mM ammonium acetateformic acid (70:30:0.1, v/v/v) at 40 ◦ C; the flow rate was set at 0.35 mL/min. The system provides the highest resolution, and best baseline stability and ionization efficiency. 3.1.2. Mass spectrometry In the Q1 full scan experiment, the ionization polarity was optimized by comparing the analyte responses in positive and negative ESI. A strong and stable MS signal for each analyte was observed in positive ionization mode. The protonated molecules of lomerizine and flunarizine were observed at m/z 469.2, and 405.2, respectively. In the product ion spectrum of lomerizine, two major fragment ions at m/z 181.0 and 203.0 were formed by neutral losses of different moieties from the [M + H]+ ion. For flunarizine, the major fragment ion was observed at m/z 202.9. The proposed mass spectral fragmentation patterns of both analytes are shown in Fig. 1. The ion transition of m/z 469.2 → m/z 181.0 provided a better signal-tonoise ratio compared with the ion transition of m/z 469.2 → m/z 203.0 and was thus selected for the quantitation of lomerizine. The turbo spray voltage was set at 5000 V, comparing with 4500 V and 5500 V, to maximize the MS responses. The dwell time for monitoring each transition was set to 200 ms. The other instrument parameters, including the collision energy (CE), declustering potential (DP), and source temperature, were carefully optimized to maximize the MS responses. 3.2. Selectivity and sensitivity Typical MRM chromatograms from the quantification of lomerizine in human plasma are shown in Fig. 2. No interfering peak was observed in the free plasma (Fig. 2A). The MRM chromatograms of blank plasma spiked with lomerizine (0.1 ng/mL), lomerizine (5.0 ng/mL), and the I.S. (10 ng/mL) are shown in Fig. 2B and Fig. 2C. A plasma sample from a volunteer after a single oral dose of 10 mg lomerizine is shown in Fig. 2D. The drug and the I.S. were free from endogenous matrix interference at their respective retention times in the chromatograms. This method had dramatically increased sensitivity (0.1 ng/mL) compared with previous studies (5 ng/mL, S/N = 3) [6] and was sufficiently sensitive for the determination and pharmacokinetic analysis of lomerizine in humans. 3.3. Linearity, carry-over, accuracy and precision The method exhibited a good linear response in the range of concentrations from 0.1 to 25 ng/mL. The regression equations of lomerizine (n = 5) in plasma were y = 0.0347x + 0.000368 (r = 0.9992), where y represents the ratio of lomerizine peak area to

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Fig. 2. Chromatograms for lomerizine (469.2 → 181.0) and I.S. (405.2 → 202.9) in (A) double blank plasma, (B) LLOQ, (C) a blank plasma sample spiked with lomerizine at 5.0 ng/mL and I.S. and (D) real subject sample.

that of the I.S. and x represents the corresponding plasma concentration. Carry-over for lomerizine was not detectable with the chosen settings. The intra- and inter-day precision and accuracy values for the QC samples are summarized in the Table 1. The intra- and interday precision (relative standard deviation, RSD) values were below 9.65% and the mean accuracy was from 99.00 to 103.00% at four Table 1 Intra- (n = 6) and inter-day (n = 6) precision and accuracy of lomerizine spiked in human plasma. Added concentration

Intraday

(ng/mL)

Mean ± SD

Mean accuracy

RSD

(ng/mL)

(%)

(%)

0.099 ± 0.010 0.201 ± 0.016 11.910 ± 0.555 20.307 ± 0.820 Interday Mean ± SD (ng/mL) 0.103 ± 0.008 0.202 ± 0.009 12.022 ± 0.503 20.080 ± 0.579

99.00 100.50 99.25 101.54

9.65 7.95 4.66 4.04

Mean accuracy (%) 103.00 101.00 100.18 100.40

RSD (%)

0.1 0.2 12 20 Added concentration (ng/mL) 0.1 0.2 12 20

7.33 4.70 4.19 2.88

quality control levels. These results indicate that the proposed method is accurate and precise. 3.4. Recovery and matrix effect The data of extraction efficiency measured for lomerizine and the I.S. in human plasma was consistent, precise, and reproducible. From Table 2, the indication from extraction procedure for the analytes was a high recovery value from their biological matrix and it was acceptable at the studied concentration range. The matrix effects for lomerizine at concentrations of 0.1, 1, and 25 ng/mL were all within 85–115%, respectively. The matrix effects for I.S. (10 ng/mL in plasma) was 88.32%. These results showed that

Table 2 Matrix effects and extraction recovery of lomerizine and flunarizine (I.S.) in human plasma. Analytes

Lomerizine

Flunarizine (I.S.)

Spiked concentration

Matrix effect

(ng/mL)

(%, mean ± SD, n = 6)

Extraction recovery (%, mean ± SD, n = 6)

0.1 1 25 10

94.31 ± 3.40 94.18 ± 1.65 91.03 ± 3.67 88.32 ± 4.10

94.73 ± 7.04 92.64 ± 2.52 93.84 ± 2.35 90.22 ± 3.10

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Table 3 Stability of lomerizine under various conditions. (n = 3). Stability

Storage condition

Level (ng/mL)

Stability in biological matrix (SBM)

Room temperature (24 h)

Autosampler stability of extracted samples (ASS)

Autosampler (20 ◦ C, 24 h)

Freeze and thaw stability (FTS)

After 3th cycle at −20 ◦ C and room temperature

Long term stability(LTS)

45 days at −20 ◦ C

0.1 1 25 0.1 1 25 0.1 1 25 0.1 1 25

Concentration Mean (ng/mL)

Accuracy %

0.093 1.042 23.814 0.097 1.047 25.826 0.104 1.072 25.933 0.102 0.971 24.558

93.00 104.20 95.26 97.00 104.70 103.30 104.00 107.20 103.73 102.00 97.10 98.23

Table 4 Pharmacokinetic parameters of lomerizine after administration of 10 mg lomerizine tablet to 18 healthy human subjects. Parameters

Mean ± SD

Cmax (ng/mL) Tmax (h) t1/2 (h) AUC0–t (ng h/mL) AUC0–∞ (ng h/mL)

9.06 ± 2.46 2.72 ± 0.91 5.48 ± 0.90 70.32 ± 15.88 74.22 ± 17.66

ion suppression or enhancement from plasma matrix was negligible in the present condition. 3.5. Dilution integrity

Fig. 3. Mean pharmacokinetic profile of lomerizine after oral administration of 10 mg lomerizine tablet to 18 healthy subjects under fasting condition (mean ± SD).

The mean back-calculated concentrations for 1/10 dilution samples were within 92.40–103.74% of their nominal values. The precision (%RSD) for 1/10 dilution samples was ≤4.50% for all the analytes. 3.6. Stability The stability of lomerizine in plasma was fully investigated. The stability experiments were aimed at testing the effects of possible conditions that the samples might experience between collection and analysis. Stability results are summarized in Table 3. Lomerizine in human plasma was found to be stable after being placed at room temperature for 24 h. Testing of auto-sampler stability of extracting samples indicated that lomerizine was stable when kept in the auto-sampler tray (20 ◦ C) for 24 h. Three cycles of freeze and thaw indicated that lomerizine was stable in plasma. Plasma samples were stable when stored frozen at −20 ◦ C for atleast 45 days. No chemical or biological degradation or decomposition of lomerizine was observed during all of the sample storage, preparation, and analysis periods. The method was therefore proved to be applicable for routine analysis. 3.7. Application of the method to pharmacokinetic study This study was conducted in compliance with the Declaration of Helsinki [16] and in accordance with Good Clinical Practice. The protocol was approved by the local ethical committee, and written informed consent and consent form were obtained for all volunteers before study participation. After single oral dose of 10 mg lomerizine, the pharmacokinetic parameters Cmax , AUC0–t and AUC0–∞ were calculated and presented in Table 4. Tmax varied from 1 h to 4 h for 18 subjects, with a median of 2.75 h. The mean plasma concentration time profile of 18 subjects of lomerizine was presented in Fig. 3. These measured pharmacokinetic parameters

Fig. 4. Graphical representation of results for 36 incurred samples of lomerizine.

were in agreement with those reported in the literature [6], indicating the applicability of this method to the pharmacokinetic study of lomerizine. 3.8. Incurred sample reanalysis The change (%) in 36 reanalyzed subject samples for incurred sample reanalysis was within −12.31–16.61%, which authenticates the reproducibility of the proposed method (Fig. 4). 4. Conclusion An HPLC–MS/MS analysis method for the quantification of lomerizine in human plasma was developed and fully validated. In our study, the desired sensitivity with an LLOQ of 0.1 ng/mL was achieved, which was proved to be superior in sensitivity in comparison to the methods reported previously. The protein precipitation sample preparation method in our study was much simpler than

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tandem mass spectrometry and its application to a pharmacokinetic study.

A rapid, sensitive and selective high performance liquid chromatography-electrospray ionization-tandem mass spectrometry method (HPLC-ESI-MS/MS) was d...
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