Determination of Pregabalin in Human Plasma Using LC-MS-MS
Transcription
Determination of Pregabalin in Human Plasma Using LC-MS-MS
Determination of Pregabalin in Human Plasma Using LC-MS-MS 2008, 67, 237–243 Uttam Mandal, Amlan Kanti Sarkar, Kadagi Veeran Gowda, Sangita Agarwal, Anirbandeep Bose, Uttam Bhaumik, Debotri Ghosh, Tapan Kumar Pal& Bioequivalence Study Centre, Department of Pharmaceutical Technology, Jadavpur University, Kolkata 32, India; E-Mail: [email protected] Received: 2 August 2007 / Revised: 25 September 2007 / Accepted: 9 October 2007 Online publication: 8 January 2008 Introduction Abstract A bioanalytical method has been developed and validated for determination of pregabalin in human plasma. The analytical method consists in the precipitation of plasma sample with trichloro acetic acid (20% v/v solution in water), followed by the determination of pregabalin by an LC-MS-MS method using gabapentin as internal standard. Separation was achieved on a Gemini C18 50 mm · 2.0 mm (3 lm) column with an isocratic mobile phase consisting of methanol–water (98:2, v/v) with 0.5% v/v formic acid. Protonated ions formed by a turbo ionspray in positive mode were used to detect analyte and internal standard. The MS-MS detection was by monitoring the fragmentation of 160.2?55.1 (m/z) for pregabalin and 172.2?67.1 (m/z) for gabapentin on a triple quadrupole mass spectrometer. The assay was calibrated over the range 0.1–15.0 lg mL 1 with correlation coefficient of 0.9998. Validation data showed intra-batch (n = 6) CV% 6.89 and RE (%) between 4.17 and +3.08 and inter-batch (n = 18) CV% < 9.09 and RE (%) between 3.0 and +10.00. Mean extraction recovery were 80.45–89.12% for three QC samples and 87.56% for IS. Plasma samples were stable for three freeze–thaw cycles, or 24 h ambient storage, or 1 and 3 months storage at 20 C. Processed sample (ready for injection) were stable up to 72 h at autosampler (4 C). This method has been used for analyzing plasma samples from a bioequivalence study with 18 volunteers. Keywords Column liquid chromatography–mass spectrometry Bioequivalence study Turbo ionspray Pregabalin Original DOI: 10.1365/s10337-007-0440-2 0009-5893/08/02 Pregabalin (PGB), (S)-3-aminomethyl-5methyl hexanoic acid, is a structural analogues of c-aminobutyric acid (GABA) as shown in Fig. 1.a. It is recently approved in the European Union (EU) as an adjunctive therapy for treatment of partial seizures with and without generalized tonic–clonic seizures and for the treatment of peripheral neuropathic pain in adults [1–8]. PGB binds potentially to the a2-d subunit, an auxiliary protein, of Q-type voltage-sensitive calcium channels that are widely distributed throughout the peripheral nervous system and CNS [9–11]. Potent binding at this site reduces calcium influx at hyperexcited nerve terminals and, therefore, reduces the release of several neurotransmitters, including glutamate, noradrenaline, and substance P [12–15]. These activities and effects result in the anticonvulsant, analgesic, and anxiolytic activity exhibited by PGB. PGB is inactive at c-aminobutyric acid (GABA)A and GABAB receptors; it is not converted metabolically into GABA or a GABA antagonist, and it does not alter GABA uptake or degradation [16, 17]. Chromatographia 2008, 67, February (No. 3/4) 2008 Friedr. Vieweg & Sohn Verlag/GWV Fachverlage GmbH 237 Table 1. Tandem mass spectrometric parameters of pregabalin and gabapentin Compound Mol. Wt. Protonated ion Fragment CE (eV) DP (V) EP (V) FP (V) CXP (V) Dwell time (ms) Pregabalin Gabapentin 159.2 171.2 160.2 172.2 55.1 67.1 35 46 19 26 10.5 10.0 398 390 1.5 2 200 200 eV Electron volt, V volt, CE collision energy, DP Declustering potential, EP entrance potential, FP focusing potential, CXP collision cell exit potential, ms milliseconds Experimental Materials and Reagents Fig. 1. Chemical structure of pregabalin and gabapentin : a pregabalin and b gabapentin PGB is not appreciably metabolized in man, and studies in healthy volunteers indicate oral bioavailability to be approximately 90% [18]. This contrasts with gabapentin, which is absorbed via a capacity-limited L-amino-acid transport system from the proximal small bowel into the blood stream [19, 20]. There are few published methods for analysis of pregabalin in human plasma by HPLC after precolumn derivatization of pregabalin using o-phtaldialdehyde (OPA) and 3-mercaptopropionic acid [21] or picrylsulfonic acid [22]. In practical application, derivatization may be a difficult technique and gives inaccurate estimation of analyte due to incomplete derivatization if reaction conditions are not strictly maintained. In comparison to precolumn derivatization for HPLC, our developed LC-MS-MS method is a simple one step precipitation, it is accurate and requires less time (2 min only) without derivatization. 238 Pregabalin (>99%) was supplied by Burgeon Pharmaceutical Pvt., Chennai, India. Gabapentin (Fig. 1b) (>99%) as internal standard (IS) was obtained from Cosmas Pharmaceuticals, Ludhiana, India. Formic acid (98%), trichloro acetic acid (analytical-reagent grade), methanol (HPLC grade) were purchased from Merck Pvt., Mumbai, India. Water (resistivity of 18 MX) was collected from a Milli-Q gradient system of Millipore (Elix 3, Milli-Q A10 Academic). The blank human plasma with EDTA-K3 anticoagulant was collected from Clinical Pharmacological Unit (CPU) of Bioequivalence Study Centre, Jadavpur University, Kolkata, India. by AB Sciex Instruments (Toronto, Canada) for detection. Sciex Analyst software version 1.4.1 was used for data acquisition and processing. Turbo ionspray ionization source was operated in a positive mode for mass spectrometric detection. The collision energy (CE) and other parameters for the analyte and IS were optimized by infusing each compound solution with a concentration of 500 ng mL 1 in water. The multiplereaction mode (MRM) was used to acquire ion counts at different time points. A high voltage of 5.5 kV was applied to the spray needle. The instrument was programmed for a scan dwell time of 200 ms. The source temperature was set at 550 C, using nitrogen (5.0 grade) at 7 L min 1 as auxiliary gas and zero grade air as nebulizer gas at a pressure of 80 p.s.i. (1 p.s.i. = 6894.76 Pa). The setting of curtain gas and collision gas flow at instrument were 10, 12 (arbitrary scale), respectively. All gas used in this experiment was generated from a Peak gas generator (Chicago, IL, USA). The collision energies and other optimized parameters used for analyte and IS are presented in Table 1. In this method, both Q1 and Q3 quadrupoles were operated at unit resolution. For each injection, the total acquisition time was 2 min. LC-MS-MS The LC system consisting of solvent delivery LC 10ADVP, Controller LC10ADVP and column oven CTO10ASVP were from Shimadzu (Kyoto, Japan). Sample injection was with a Shimadzu SIL HTC Autosampler. The analytical column used was a Gemini C18 50 mm · 2.0 mm (3 lm) from Phenomenex, USA. Elution was achieved at room temperature with methanol–water (98:2, v/v), 0.5% v/v formic acid as the mobile phase. The LC system was operated isocratically at 1 mL min 1. The column eluent was split and approximately 400 lL were introduced in the mass spectrometer. The total run time for each sample analysis was 2 min only. The LC system was coupled with a turbo ionspray ionization-triple quadrupole mass spectrometer API 2000 made Standard Solutions and Quality Control (QC) Samples The stock solutions of analyte and IS were prepared at 1 mg mL 1 in water by vortexing approximately 1 min. Dilutions of 100 and 10 lg mL 1 were made from the stock solutions which were used to prepare the calibration curve and quality control (QC) samples. An eight-point standard curve was prepared by spiking the blank plasma with appropriate amounts of working solution to obtain final concentrations of 0.1, 0.25, 0.5, 1, 2.5, 5, 10 and 15 lg mL 1 for the analyte. The concentration of IS in plasma sample was 5.0 lg mL 1. All stock solutions and working standard solutions were stored in polypropylene vials in a 20 C freezer. Chromatographia 2008, 67, February (No. 3/4) Original 4.3e5 160.2 (a) 182.1 4.0e5 3.5e5 3.0e5 Intensity (cps) The linear regression of the peak area ratio of analyte/IS versus concentration using a weighed 1/concentration2 was used to obtain the calibration curve. The regression equation of the calibration curve was then used to calculate the plasma concentration. The back calculated values of the concentrations were statistically evaluated. Quality control samples were made using the stock solution. Four levels of QC samples in plasma were 0.050 (lower limit of quantitation, i.e. LLOQ), 0.3 (low-), 6.0 (medium-), and 12.0 (high-) lg mL 1 for the analyte. QC samples were prepared in a 50 mL pool then aliquoted into pre-labeled 2 mL polypropylene vials and stored at 20 C. 2.5e5 2.0e5 119.3 201.2 1.5e5 142.2 1.0e5 161.0 199.2 151.0 171.1 176.9 183.0 204.0 143.2 157.9 164.9 141.1 104.9 200.2 180.9 129.0 147.1 179.0 184.9 108.9 115.9 125.2 205.1 193.0 173.0 145.1 164.0 149.9155.0 132.0136.2 188.8 107.1 114.0 5.0e4 149.0 117.2 130.9 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 m/z (amu) 172.0 2.6e5 Sample Preparation Method Validation The method was validated for selectivity, linearity, precision, accuracy, recovery and stability according to the principles of the Food and Drug Administration (FDA) industry guidance [23]. Three validation batches were processed on three separate days. Each batch included one set of calibration standards and six replicates of LLOQ, low-, medium-, and high-concentrations of QC samples. Inter-batch and intra-batch precision Original 2.4e5 2.2e5 2.0e5 1.8e5 Intensity (cps) For calibration standards, an aliquot of 0.1 mL for each spiking solution was spiked into 0.9 mL of control blank plasma in polypropylene tube. Then 0.1 mL of IS working solution was added to each tube and all the samples were vortex-mixed for 30 s. Then 0.2 mL of trichloro acetic acid (20% v/v solution in water) was added followed by 10 min mixing by cyclo mixer. All the samples were centrifuged for 15 min at 5,000 rpm. The supernatant clear solution was separated and filtered through a 0.45 lm membrane filter. The resulting samples were transferred into a 1.0 mL glass vial which was loaded into the autosampler cabinet and 20 lL aliquot of each extracted sample was injected into the LC-MS-MS system. (b) 1.6e5 149.0 1.4e5 1.2e5 153.9 1.0e5 119.0 8.0e4 6.0e4 4.0e4 2.0e4 176.9 180.9 130.9 160.9 137.2 176.0 129.1 115.2 162.9 173.0 151.0 156.9 117.1 178.9 105.1 147.0 113.1 127.9 114.1 180.0 183.1 145.0 159.9 166.9 121.1 134.9139.1 185.0 149.9 157.9 106.2 170.9 145.9 131.9 112.2 120.2123.8125.0 167.9 103.1 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 m/z (amu) Fig. 2. Parent ion mass spectra: a pregabalin (m/z 160.2) and b gabapentin (m/z 172.2) and accuracy evaluations were based on back-calculated concentrations. The selectivity is the ability of an analytical method to differentiate and quantify the analyte in the presence of other components in the sample. This test was performed by analyzing the blank plasma samples from different sources (or doners) to test for interference at the retention time of pregabalin and gabapentin (IS). The recovery of pregabalin (low-, medium- and high-QC) and gabapentin (5.0 lg mL 1) from human plasma were evaluated by comparing the peak area response of precipitated analyte and internal standard with that of reference solutions at the same concentration level and reconstituted into blank plasma extracts. The number of replicates for each concentration was six. Stability study was evaluated as part of the method validation. The processed sample stability was evaluated by comparing the precipitated samples that were injected immediately (time 0), with the samples that were re-injected after loading into the autosampler at 4 C for 72 h. QC samples were kept at ambient temperature for 24 h and analyzed against freshly spiked standard curve and QC samples for short-time stability. The longterm stability of spiked human plasma stored at 20 C was evaluated by Chromatographia 2008, 67, February (No. 3/4) 239 pregabalin sample time and to infinity (AUC0-t and AUC0-inf), maximum concentration (Cmax), time to maximum concentration (tmax), elimination rate constant (Kel) and elimination half-life (t1/2) were determined for the period of 0–24 h by non compartmental method. Results and Discussion Mass Spectrometry LC-MS-MS for the determination of pregabalin in human plasma was investigated. Positive electrospray mass spectra of pregabalin shows an intense [M + H] + ion at m/z 160.2 (Fig. 2a). Another intense [M + H]+ ion at m/z 172.2 is shown for gabapentin (Fig. 2b). When these molecular ions undergo fragmentation in the collision cell, the product ion mass spectra shown in Fig. 3a and b are generated. With the experimental conditions used in these experiments, pregabalin shows an intense product ion at m/z 55.1 which corresponds to the positively ionized fragment given below: Fig. 3. Product ion mass spectra: a pregabalin (m/z 55.1) and b gabapentin (m/z 67.1) analyzing all QC samples that were stored at 20 C for 1 and 3 months together with freshly spiked standard curve and QC samples. The freeze–thaw stability was conducted by comparing the stability samples that had been frozen and thawed three times, with the plasma samples thawed once. Three aliquots of each QC sample were used for freeze–thaw stability evaluation. All stability evaluations were based on back-calculated concentrations. Application The above-mentioned validated method was successfully used to analyze plasma samples for a bioequivalence study of 240 pregabalin. The study was approved by the ethics committee of Jadavpur University, Kolkata, India. It was an open, randomized crossover study to determine relative bioavailability of pregabalin in eighteen healthy male volunteers following single dose administration of pregabalin 300 mg capsule. Test preparation was pregabalin 300 mg capsule manufactured by Burgeon Pharmaceutical Pvt., Chennai, India. Capsule Newgaba containing 300 mg of pregabalin, manufactured by Sun Pharma Industries Pvt., Mumbai, India was used as reference preparation. The pharmacokinetic parameters like area under the plasma-concentration–time curve from zero to the last measurable The product ion mass spectrum of gabapentin shows an intense fragmentation at m/z 67.1 that corresponds to an ionic fragment shown below: Separation and Specificity Typical MRM chromatograms from the study of pregabalin and gabapentin in human plasma are shown in Fig. 4b. Retention time of pregabalin and IS are at 0.79 and 0.53 min, respectively. No interference peak was found in the MRM profiles for six blank plasma samples (Fig. 4a). Chromatographia 2008, 67, February (No. 3/4) Original Limit of Quantitation, Linearity (a) Intensity (cps) Lower limit of quantitation was established as 50 ng mL 1, its precision (CV%) and accuracy (%RE) values being 10.59 and 9.83%, respectively. The equation of the calibration curve was obtained by least-squares linear regression analysis of the peak-area ratios of pregabalin to internal standard versus concentration. The curve was linear in the concentration range 0.10– 15.00 lg mL 1 with regression coefficient of 0.9998 (calibration equation, y = 0.192x + 0.0158). The average correlation coefficient was 0.9998. All back calculated values showed excellent accuracy and precision (Table 2). No single calibration standard point was dropped during the validation. Time (min) 2.1e5 0.79 (b) PREGABALIN 2.0e5 1.8e5 1.6e5 Precision and Accuracy Intensity (cps) 1.4e5 The precision and accuracy of QC samples are presented in Table 3. For low-, medium-, and high-QC samples validation data showed the intra-batch (n = 6) CV% 6.89 and RE (%) between 4.17 and +3.08 and inter-batch (n = 18) CV% < 9.09 and RE (%) between 3.0 and +10.00. These results indicate that the method was reliable within the analytical range. GABAPENTIN(I.S.) 1.2e5 0.53 1.0e5 8.0e4 6.0e4 4.0e4 2.0e4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time (min) Recovery Six replicates of three QC samples were prepared for recovery determination. Mean (CV%) absolute recovery for pregabalin at 0.30, 6.00 and 12.00 lg mL 1 were 80.45% (6.11), 83.19% (4.26) and 89.12% (3.08), respectively. Mean (CV%) recovery of internal standard (5.00 lg mL 1) was 87.56% (4.92). Stability Each stability test included six replicates of three levels of QC samples. All stability results, as well as the linear regression correlation coefficients of calibration curves generated from each Original Fig. 4. Representative MRM chromatogram of pregabalin and gabapentin (IS): a blank human plasma; b Plasma sample of a volunteer showing separation of pregabalin (0.79 min) and gabapentin (IS) (0.53 min) after oral administration of capsule containing 300 mg of pregabalin Table 2. Summary of calibration standards Conc. added (lg mL 1) 0.10 0.25 0.50 1.00 2.50 5.00 10.00 15.00 Conc found (lg mL 1) SD CV (%) RE (%) n 0.11 0.24 0.53 0.93 2.63 5.15 9.75 14.41 0.01 0.02 0.04 0.06 0.15 0.39 0.4 9 0.68 9.09 8.33 7.55 6.45 5.70 4.82 5.02 4.72 +10.00 4.00 +6.00 7.00 +5.20 +3.00 2.50 3.93 6 6 6 6 6 6 6 6 SD Standard deviation, CV (%) coefficient of variation [(SD/Mean) · 100], RE (%) relative error [{(Conc. Found Conc. Added)/Conc. Added} · 100], n number of replicates stability test run for the analyte are presented in Table 4. QC samples undergoing three freeze–thaw cycles gave % CV 6.41 and an accuracy of 92.81–98.27%. QC samples storing at ambient for 24 h gave 5.75% CV and Chromatographia 2008, 67, February (No. 3/4) 241 Application Table 3. Precision and accuracy for pregabalin Conc. added (lg mL 1) Intra-batch 0.30 6.00 12.00 Inter-batch 0.30 6.00 12.00 Conc found (lg mL 1) SD CV (%) 0.29 5.75 12.37 0.02 0.31 0.53 6.89 5.39 4.28 3.33 4.17 +3.08 6 6 6 0.330 5.92 11.64 0.03 0.35 0.72 9.09 5.91 6.19 +10.00 1.33 3.00% 18 18 18 RE (%) n SD Standard deviation, CV (%) coefficient of variation [(SD/Mean) · 100], RE (%) relative error [{(Conc. Found Conc. Added)/Conc. Added} · 100], n number of replicates Table 4. Short-term and long-term stability data Storage Condition Low-QC (0.300 lg mL 1) Medium-QC (6.0 lg mL 1) High-QC (12.0 lg mL 1) r2 3 Freeze/thaw cycle 24 h ambient 72 h at autosampler 1 month frozen ( 20 C) 3 month frozen ( 20 C) 92.81 93.61 96.49 94.23 92.29 96.43 96.18 97.52 97.11 96.41 98.27 (5.25) 97.84 (2.23) 100.19 (4.72) 98.45 (1.97) 97.01 (2.40) 0.9998 0.9982 0.9978 0.9995 0.9989 (6.41) (5.75) (2.68) (6.19) (6.87) (3.17) (3.87) (2.98) (4.42) (3.66) The data presented in this table are the percentage of measured value vs. theoretical value with CV in parenthesis (n = 6). r2 is the linearity of the calibration curve used for this treatment The above-mentioned LC-MS-MS method was used in the plasma sample analysis for a bioequivalence study of pregabalin as described above. Figure 5 shows the mean (±SD) plasma level of pregabalin for test and reference preparation after the oral administration of a single dose 300 mg capsule of pregabalin in 18 healthy human volunteers. Maximum plasma concentration (Cmax) ranged from 6.925 to 7.477 lg mL 1 at 1.86–2.12 h (tmax). The elimination half life (t1/2) ranged from 3.99 to 5.33 h with elimination rate constant (Kel) of 0.096– 0.185. Also the mean value of area under the concentration time curve (AUC0-t) obtained was 43.079–48.768 lg h mL 1 and AUC0-inf was found to be 45.252– 57.446 lg h mL 1. Relative bioavailability of test preparation was 93.67% to that of reference preparation and both the products were bioequivalent. Conclusions Fig. 5. Mean (±SD) plasma concentration of pregabalin following 300 mg oral dose of test and reference preparation to 18 healthy human volunteers an accuracy of 93.61–97.84%. Processed samples (ready for injection) were found to be stable for at least 72 h at 4 C in the autosampler with %CV of 4.72% and accuracy of 96.49–100.19%. Long term frozen storage stability was tested at 1 and 3 month after QC sample pools were prepared and stored 242 at 20 C. The 1-month stability data of all three QC samples showed an accuracy of 94.23–98.45% (CV% 6.19) in comparison with their theoretical values in plasma samples. The 3-month stability data of all three QC samples had an accuracy of 92.29–97.01% (% CV 6.87) in plasma. The LC-MS-MS method described here has significant advantages over the other techniques already described in the literature [21, 22]. The method has proved to be fast with each sample requiring a run time of 2 min only and therefore has a high throughput capability. The assay method is specific due to the inherent selectivity of tandem mass spectrometry. The major advantage of this method is the simple one step precipitation for sample preparation. The proposed method to analyze pregabalin in plasma by LC-MS-MS method happens to be first of its kind described so far in the literature. This new method will be helpful for carrying out pharmacokinetic study. 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