Liquid chromatographic-electrospray tandem mass spectrometric method for the quantification of nimodipine in human plasma

A simple, sensitive and rapid liquid chromatography/electrospray ionization tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of nimodipine, a calcium channel blocker, in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reverse phase C18 column and analyzed by MS in the multiple reaction monitoring mode using the respective [M + H]+ ions, m/z 419/343 for nimodipine and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 0.2-50 ng/mL for nimodipine in human plasma. The lower limit of quantification was 200 pg/mL with a relative standard deviation of less than 8%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 3 min for each sample made it possible to analyze more than 250 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.     

Liquid chromatographic tandem mass spectrometry method for the quantification of miglitol in human plasma

A rapid, sensitive and accurate liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of miglitol (CAS 72432-03-2), an alpha-glucosidase inhibitor, in human plasma using gabapentin (CAS 60142-96-3) as internal standard (IS). Following protein precipitation, the analytes were separated using an isocratic mobile phase on a reversed phase phenyl column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 208/146 for miglitol and m/z 172/154 for the IS. The assay exhibited a linear dynamic range of 100-6000 ng/mL for miglitol in human plasma. The lower limit of quantification was 100 ng/mL with a relative standard deviation of less than 5 %. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. The average absolute recoveries of miglitol and the IS from spiked plasma samples were 40.5 +/- 2.7 and 47.1 +/- 2.9 %, respectively. A run time of 2.5 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies. The miglitol plasma concentration profile could be obtained for pharmacokinetic study. The observed maximum plasma concentration (Cmax) of miglitol (100 mg oral dose) is 1740 ng/mL, time to observed maximum plasma concentration (tmax) is 3.5 h and elimination half-life (t(1/2)) is 2.5 h.     

Quantification of metaxalone in human plasma by liquid chromatography coupled to tandem mass spectrometry

A simple, rapid, sensitive, and selective liquid chromatography-tandem mass spectrometry (MS) method was developed and validated for the quantification of metaxalone, a skeletal muscle relaxant, in human plasma using galantamine as internal standard (IS). Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reverse phase C18 column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 222/161 for metaxalone and m/z 288/213 for the IS. The assay exhibited a linear dynamic range of 50-5000 microg/L for metaxalone in human plasma. The lower limit of quantification was 50 microg/L with a relative standard deviation of less than 10%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability, or bioequivalence studies.     

Rapid quantification of gabapentin in human plasma by liquid chromatography/tandem mass spectrometry

A simple, sensitive and rapid liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of gabapentin, a new antiepileptic drug, in human plasma using its structural analogue, 1,1-cyclohexane diacetic acid monoamide (CAM) as internal standard. The method involved a simple protein precipitation by means of acetonitrile followed by a rapid isocratic elution with 10mM ammonium formate buffer/acetonitrile (20/80, v/v, pH 3.0) on Waters Symmetry C(18 reversed phase chromatographic column and analyzed by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 172-->154 and m/z 200-->182 were used to measure the analyte and the IS, respectively. The assay exhibited a linear dynamic range of 40-10000 ng/mL for gabapentin in human plasma. The limit of detection and lower limit of quantification in human plasma were 10 and 40 ng/mL, respectively. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 2 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.     

High performance liquid chromatography-tandem mass spectrometric determination of rupatadine in human plasma and its pharmacokinetics

A simple, rapid, sensitive and selective liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method was developed and validated for the quantification of rupatadine in human plasma using estazolam as internal standard (IS). Following liquid-liquid extraction, the analytes were separated using a mobile phase of methanol-ammonium acetate (pH 2.2; 5mM) (50:50, v/v) on a reverse phase C18 column and analyzed by a triple-quadrupole mass spectrometer in the positive ion and multiple reaction monitoring (MRM) mode, m/z 416-->309 for rupatadine and m/z 295-->267 for the IS. The assay exhibited a linear dynamic range of 0.1-100 ng/ml for rupatadine in human plasma. The lower limit of quantification (LLOQ) was 0.1 ng/ml with a relative standard deviation of less than 20%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The validated LC-MS/MS method has been successfully applied to study the pharmacokinetics of rupatadine in healthy volunteers.     

Quantitative determination of rosuvastatin in human plasma by ion pair liquid-liquid extraction using liquid chromatography with electrospray ionization tandem mass spectrometry

A simple and sensitive liquid chromatography/tandem mass spectrometry method was developed and validated for the quantification of rosuvastatin in human plasma. After being treated with acetic acid and tetrabutyl ammonium hydroxide, the analyte was extracted by simple one-step liquid-liquid extraction with the internal standard (IS: estrone). The chromatographic separation was performed on a Phenomenex Luna C18 column with a mobile phase consisting of 2% formic acid/methanol (20:90, v/v) at a flow rate of 1.00 mL/min with a split of 200 microL to mass spectrometer. The retention time of rosuvastatin and internal standard was 2.3 and 3.4 min, respectively. Triple-quadrupole MS/MS detection was operated in positive mode by monitoring the transition of m/z 482-->258 for rosuvastatin and m/z 271-->253 for IS. Validation results indicated that the lower limit of quantification (LLOQ) was 0.1 ng mL(-1) and the assay exhibited a linear range of 0.1-20 ng mL(-1) and gave a correlation coefficient (r) of 0.9990 or better. Inaccuracy was less than 8.4% and imprecision less than 12.8% at all tested concentration levels. The analyte was stable in human plasma following three freeze/thaw cycles and for up to 8 weeks following storage at -20 degrees C. The assay was successfully applied to the analysis of rosuvastatin in human plasma samples derived from clinical pre-trials.     

Simultaneous quantification of losartan and active metabolite in human plasma by liquid chromatography–tandem mass spectrometry using irbesartan as internal standard

A simple and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) method employing electronspray ionization was developed and validated for quantification of losartan and its carboxylic acid metabolite in human plasma using irbesartan as internal standard (IS). Following a simple pretreatment procedure, the analytes were separated using a gradient mobile phase on reverse phase C₁₈ column. Selected reaction monitoring was specific for losartan, losartan acid and irbesartan. The method validation demonstrated the specificity, lower limit of quantification, accuracy and precision of measurements. The assay exhibited a linear dynamic range of 2.0–400 ng/mL for losartan and 1.85–370 ng/mL for losartan acid. A run time of 3.5 min for each sample made it possible to analyze more than 200 samples per day. The validated method has been successfully used to analyze human plasma samples for application in bioavailability/bioequivalence studies.     

Determination of moxonidine in human plasma by liquid chromatography-electrospray ionisation-mass spectrometry

A sensitive and specific liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) method has been developed and validated for the identification and quantification of moxonidine in human plasma. After the addition of clonidine-HCl, the internal standard (IS) and sodium hydrogen carbonate, plasma samples were extracted using 5 mL ethyl acetate. The compounds were separated on a Lichrospher ODS (5 microm, 250 mm x 4.6 mm) column using an elution system of 10 mmol/L ammonium acetate buffer-methanol (20:80 v/v) as the mobile phase. Analytes were determined using electrospary ionization in a single quadrupole mass spectrometer. LC-ESI-MS was performed in the selected-ion monitoring (SIM) mode using target ions at m/z: 242.2 for moxonidine and m/z: 230.1 for the IS. The method has shown to be sensitive and specific by testing six different blank plasma batches. Linearity was established for the range of concentrations 0.01976-9.88 ng/mL with a coefficient of correlation (r) of 0.9999. The lower limit of quantification (LOQ) was identifiable and reproducible at 0.01976 ng/mL. The method has been successfully applied to study the pharmacokinetics of moxonidine in healthy male Chinese volunteers.     

A simple and sensitive gradient elution liquid chromatography with tandem mass spectrometry (LC-MS/MS) method for the quantification of doxorubicin in rabbit plasma

In the present study, we developed and validated a simple and sensitive gradient elution liquid chromatography tandem mass spectrometry (LC-MS/MS) method for quantification of doxorubicin in rabbit plasma. Daunorubicin was used as an internal standard (IS). The doxorubicin and IS were extracted with ethyl acetate from plasma samples. The chromatographic separations were achieved on a C₁₈ column (2.1 mm×50 mm, 2.5 μm) configured with a C₁₈ guard column (2.1 mm×10 mm, 2.5 μm). The mobile phase of 0.1% formic acid-water solution and acetonitrile was delivered using a gradient elution program at a flow rate of 0.4 mL/min. The temperature for column was maintained at 40 ºC. The electrospray ionization (ESI) source was operated in the positive ion mode, and the quantification was conducted using multiple reaction monitoring (MRM) of the transitions m/z 544.07→396.96 and m/z 528.06→321.05 for doxorubicin and IS, respectively. The calibration curve of doxorubicin was linear (r > 0.999) within the range of 2-600 ng/mL. The lower limit of quantification was 2 ng/mL. The relative errors of intra­day and inter-day accuracies ranged from -2.48% to 0.18% and from -3.78% to 1.94%, respectively. The relative standard deviations of intra­day and inter-day precisions were less than 8.65% and 6.41%, respectively. The method exhibited satisfactory results in terms of specificity, sensitivity, matrix effect, recovery and stability. The newly developed LC-MS/MS method was reliable to monitor doxorubicin concentrations in rabbit plasma.     

Determination of cetirizine in human plasma using high performance liquid chromatography coupled with tandem mass spectrometric detection: application to a bioequivalence study

A rapid, sensitive and selective HPLC-MS/ MS method was developed and validated for the quantification of cetirizine dihydrochloride (CAS 83881-51-0) in human plasma using mosapride citrate as internal standard (IS, CAS 112885-42-4). Following liquid-liquid extraction, the analytes were separated using a mobile phase consisting of methanol and aqueous ammonium acetate solution (10 mM) (60:40, v/v) on a reverse phase C18 column and analyzed by a triple-quadrupole mass spectrometer in the selected reaction monitoring (SRM) mode using the respective [M+H]+ ions, m/z 398 --> 201 for cetirizine and m/z 422 --> 198 for mosapride. The analysis time for each run was 8.0 min. The assay exhibited a linear dynamic range of 0.5-500 ng/ml for cetirizine dihydrochloride in human plasma. The lower limit of quantification (LLOQ) was 0.5 ng/ml with a relative standard deviation of less than 15% (all the concentration data in this study related to the salt (cetirizine dihydrochloride)). Acceptable precision and accuracy were obtained for concentrations over the standard curve range. It is the first time that the validated HPLC-MS/MS method has been successfully applied to a bioequivalence study in 20 healthy male Chinese volunteers.     

Simultaneous determination of amoxicillin and ambroxol in human plasma by LC-MS/MS: validation and application to pharmacokinetic study

A rapid, simple and sensitive LC-MS/MS method was developed for simultaneous determination of amoxicillin and ambroxol in human plasma using clenbuterol as internal standard (IS). The plasma samples were subjected to a simple protein precipitation with methanol. Separation was achieved on a Lichrospher C(18) column (150 mm x 4.6mm ID, dp 5 microm) using methanol (containing 0.2% of formic acid) and water (containing 0.2% of formic acid) as a mobile phase by gradient elution at a flow rate of 1.0 mL/min. Detection was performed using electrospray ionization in positive ion multiple reaction monitoring (MRM) mode by monitoring the ion transitions from m/z 365.9-->348.9 (amoxicillin), m/z 378.9-->263.6 (ambroxol) and m/z 277.0-->203.0 (IS). Calibration curves were linear in the concentration range of 5-20,000 ng/mL for amoxicillin, and 1-200 ng/mL for ambroxol, with the intra- and inter-run precisions of <9% and the accuracies of 100+/-7%. The method has been validated and applied to pharmacokinetic studies of compound amoxicillin and ambroxol hydrochloride tablets in healthy Chinese volunteers.     

Determination of domperidone in human plasma using liquid chromatography coupled to tandem mass spectrometry and its pharmacokinetic study

A sensitive and selective liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of domperidone (CAS number: 57808-66-9) in human plasma using paracetamol (CAS number: 103-90-2) as an internal standard (IS). Domperidone and paracetamol in plasma were extracted with ethyl acetate, separated on a C18 reversed phase column, eluted with mobile phase of acetonitrile-glacial acetic acid (0.3%) (40:60, v/v), ionized by positive ion pneumatically assisted electrospray and detected in the multi-reaction monitoring mode using precursor→product ions of m/z 426.2→175.1 for domperidone and 152→110 for the IS, respectively. The calibration curve was linear (r2≥0.99, n=5) over the concentration range of 0.2-80 ng/mL and with lower limit of detection and quantitation of 0.05 and 0.2 ng/mL. The speci?city, matrix effect, recovery, sensitivity, linearity, accuracy, precision, and stabilities were validated for domperidone in human plasma. In conclusion, the validation results showed that this method was sensitive, economical and less toxic and it can successfully ful?ll the requirement of clinical pharmacokinetic study of domperidone oral preparation in Chinese healthy volunteers.     

Development and validation of a liquid chromatography-isotope dilution tandem mass spectrometry for determination of olanzapine in human plasma and its application to bioavailability study

A simple, reliable and sensitive liquid chromatography-isotope dilution mass spectrometry (LC-ID/MS) was developed and validated for quantification of olanzapine in human plasma. Plasma samples (50 microL) were extracted with tert-butyl methyl ether and isotope-labeled internal standard (olanzapine-D3) was used. The chromatographic separation was performed on XBridge Shield RP 18 (100 mm x 2.1 mm, 3.5 microm, Waters). An isocratic program was used at a flow rate of 0.4 m x min(-1) with mobile phase consisting of acetonitrile and ammonium buffer (pH 8). The protonated ions of analytes were detected in positive ionization by multiple reactions monitoring (MRM) mode. The plasma method, with a lower limit of quantification (LLOQ) of 0.1 ng x mL(-1), demonstrated good linearity over a range of 0.1 - 30 ng x mL(-1) of olanzapine. Specificity, linearity, accuracy, precision, recovery, matrix effect and stability were evaluated during method validation. The validated method was successfully applied to analyzing human plasma samples in bioavailability study.     

Determination and pharmacokinetics of danshensu in rat plasma after oral administration of danshen extract using liquid chromatography/tandem mass spectrometry.

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated for the determination and pharmacokinetics of danshensu in rat plasma samples using ferulic acid as internal standard (IS). The plasma samples were treated by liquid-liquid extraction, and the analyses were determined using electrospray negative ionization mass spectrometry in selected reaction monitoring (SRM) mode. The signal intensity of the m/z 196.8 --> 134.8 transition of danshensu was found to relate linearly to danshensu concentrations in the plasma from 5-500 ng/mL. The lower limit of quantification (LLOQ) as determined by the LC/MS/MS method amounted to 5 ng/mL. The intra- and inter-day precision was below 10.82%, and the accuracy was between -3.51% and +11.92%. The validated LC/MS/MS method was applied to a pharmacokinetic study in which danshen extract (containing 40 mg/g danshensu) was administered orally to rats at a single dose of 200 mg/kg in 2% water.     

Quantification of azithromycin in human plasma by liquid chromatography tandem mass spectrometry: application to a bioequivalence study

A specific, sensitive and rapid liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method has been developed and validated for the determination of azithromycin in human plasma. After deproteinizing the plasma sample with methanol, azithromycin and internal standard (IS: roxithromycin) were separated using a mobile phase comprised of acetonitrile : ammonium acetate buffer (50 mM, containing 0.05% acetic acid)=85:15 on a Hypersil GOLD C18 column (50 mm×2.1 mm ID, dp 1.9 μm). Detection was performed with a tandem mass spectrometer by selective reaction monitoring (SRM) through electrospray ionization. Target ions were monitored at [M+H]+ m/z 749.5→591.5 and 837.7→679.5 in positive electrospray ionization (ESI) mode for azithromycin and IS respectively. Linearity was established for the range of concentrations 2-800 ng/mL with a coefficient of correlation (r) of 0.9996. The lower limit of quantification (LLOQ) was identifiable and reproducible at 2.0 ng/mL. Both intra- and inter-batch standard deviations were less than 15%. The validated method was successfully applied to study the comparative bioavailability of azithromycin for suspension in test vs. reference in healthy Chinese volunteers through the statistical comparison of pharmacokinetic parameters obtained with the two formulations.     

Development and validation of a liquid chromatography with tandem mass spectrometry (LC-MS/MS) method for the determination of sunitinib in rabbit plasma

A liquid chromatography with tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the measurement of sunitinib in rabbit plasma. After protein precipitation with acetonitrile, samples were analyzed on a Zorbax Extend-C₁₈ column (150 mm×4.6 mm, 5μm). The mobile phase consisted of a mixture of acetonitrile and deionized water (containing 0.05% formic acid)at a ratio of 27:73 (v/v), and the flow rate was set at 0.8 mL/min.The column temperature was maintained at 30 ^oC. The LC eluate was detected by an electrospray ionization (ESI) source operated in the positive ion mode, and quantification was conducted using MRM of the transitions m/z 399.24→283.01 and m/z 415.19→178.00 for sunitinib and internal standard (IS, diltiazem hydrochloride), respectively. The calibration curve was linear in the range of 2–600 ng/mL. The lower limit of quantification was 2 ng/mL. The method also exhibited satisfactory results in terms of sensitivity, specificity, accuracy (with relative error ranging from –4.0% to 1.1%), precision (with intra- and inter-day relative standard deviations ranging from 2.8% to 9.5%),matrix effect, recovery as well as stability. Taken together, our newly developed method was reliable to monitor sunitinib concentrations in rabbit plasma.     

In vitro plasma protein binding determination of flunarizine using equilibrium dialysis and liquid chromatography-tandem mass spectrometry

A highly sensitive method was developed and validated for determining the free fraction of flunarizine in human plasma. Equilibrium dialysis was used for the separation of free (unbound) drug and liquid chromatography/tandem mass spectrometry (LC-MS/MS) was used for quantitation. Post-dialysis plasma or buffer samples of 0.2 mL were extracted using a liquid-liquid extraction procedure and analyzed using a high performance liquid chromatography electrospray tandem mass spectrometer system. The compounds were eluted isocratically on a Supelco Supelcosil ABZ+Plus column, ionized using a positive ion atmospheric pressure electrospray ionization source, and analyzed using multiple reaction monitoring. The ion transitions monitored were m/z 405-->203 for flunarizine and m/z 409-->207 for flunarizine-d4 (internal standard, IS). The chromatographic run time was 3.5 min per injection, with retention times of 2.1 min for both flunarizine and IS. The calibration curve for flunarizine was linear over the concentration range of 0.25-2000 ng/mL (r(2)>0.9989) in the combined matrix of human plasma and isotonic sodium phosphate buffer (1:1, v/v) with the lower limit of quantitation of 0.25 ng/mL. The inter-assay coefficient of variability (CV) for the quality control samples was less than 13.5%, and the inter-assay percent nominal was greater than 98.2%. In vitro protein binding of flunarizine was determined at concentrations of 5, 10 and 100 microg/mL using the validated method. Flunarizine was extensively bound to plasma protein with a 0.083+/-0.005% overall percent free drug in plasma and a CV value less than 7.8%. This validated method will be used for the ex vivo assessment of flunarizine protein binding in human plasma from a drug-drug interaction clinical study.     

A rapid and sensitive liquid chromatography-tandem mass spectrometry method for determination of olopatadine concentration in human plasma

A sensitive and rapid method based on liquid chromatography- tandem mass spectrometry (MS-MS) was developed for the determination of olopatadine in human plasma. Sample preparations were carried out by protein precipitation with the addition of acetonitrile followed by liquid-liquid extraction with ethyl acetate/dichloromethane after internal standard (IS, amitriptyline) spiked. After evaporation to dryness, the resultant residue was reconstituted in mobile phase. Separation of olopatadine and IS from the interferences was achieved on a C(18) column followed by MS-MS detection. The analytes were monitored in the positive ionization mode with a TurboIonspray source. Multiple reaction monitoring using the transition of m/z 338 → 165 and m/z 278 → 91 was performed to quantify olopatadine and IS, respectively. The method had a total chromatographic run time of 3.5 min and linear calibration curves over the concentration range of 0.2-100 ng/mL. The lower limit of quantification was 0.2 ng/mL. For each QC concentration level the intra- and interday precisions were less than 11.4%, and relative errors ranged between -6.40% and 9.26%. The validated method was successfully applied to the quantification of olopatadine concentration in human plasma after administration of olopatadine at an oral dose of 5 mg in order to evaluate the pharmacokinetics.     

Rapid and simultaneous measurement of midazolam, 1'-hydroxymidazolam and digoxin by liquid chromatography/tandem mass spectrometry: application to an in vivo study to simultaneously measure P-glycoprotein and cytochrome P450 3A activity

In order to simultaneously determine in vivo P-glycoprotein (P-gp) and Cytochrome P450 3A (CYP3A) activity, a new, rapid and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and fully validated to simultaneously determine midazolam (MDZ, as CYP3A substrate), 1'-hydroxymidazolam (1'-OHMDZ) and digoxin (DG, as P-gp substrate) in rat plasma using digitoxin as the internal standard (IS). After a single step liquid-liquid extraction with tert-butyl methyl ether/dichloromethane (75:25, v/v), analytes were subjected to LC-MS/MS analysis using positive electro-spray ionization (ESI(+)) under selected reaction monitoring mode (SRM). Chromatographic separation was performed on an XTerra MS C18 column (50mm×2.1mm, i.d. 3.5μm). The MS/MS detection was conducted by monitoring the fragmentation of 326.05 → 244.00 (m/z) for MDZ, 342.02 →168.01 (m/z) for 1'-OHMDZ, 798.33 → 651.36(m/z) for DG and 782.67 → 635.24 (m/z) for IS. The method had a chromatographic running time of 3min and linear calibration curves over the concentrations of 2-400ng/mL for MDZ and 1'-OHMDZ and 0.5-100ng/mL for DG. The recoveries of the method were 86.8-96.3% for MDZ, 84.6-86.4% for 1'-OH MDZ, and 81.7-85.1% for DG. The lower limit of quantification (LLOQ) of the method was 2ng/mL for MDZ and 1'-OHMDZ and 0.5ng/mL for DG. The intra- and inter-batch precision were less than 15% for all quality control samples at concentrations of 5, 50 and 320ng/mL for MDZ and 1'-OHMDZ and 1, 10 and 80ng/mL for DG. The validated LC-MS/MS method has been successfully used to analyze the concentrations of MDZ, 1'-OH MDZ and DG in rat plasma for simultaneous measurement of in vivo P-gp and CYP 3A activity.     

Quantification of levetiracetam in human plasma by liquid chromatography-tandem mass spectrometry: application to therapeutic drug monitoring

A rapid, selective, reliable, precise, accurate, and reproducible tandem mass spectrometric (MS-MS) method for the quantification of levetiracetam (LEV) in human plasma using adenosine as an internal standard (IS) has been developed and validated. The drug and IS were extracted by solid phase extraction (SPE) technique and analyzed on Symmetry((R)) C(18) column (5 microm, 3.9 mm x 50 mm) using a mobile phase of methanol-water-formic acid (97:03:0.25, v/v/v) at a flow rate of 0.2 ml/min. Quantitation was achieved using a positive electrospray ionization (ESI+) interface employing multiple reaction monitoring (MRM) mode at MRM transitions m/z 171>126 and m/z 268>136 for LEV and IS, respectively. The method was validated over the concentration range of 1.0-40 microg/ml (r>0.99) with a limit of quantification of 1.0 microg/ml (R.S.D.%; 4.1 and Bias%; -9.0 to + 11.0%). Intra- and inter-run precision of LEV assay at three concentrations ranged from 0.6 to 8.9% with accuracy (bias) varied from -4.0 to 8.6% indicating good precision and accuracy. Analytical recoveries of LEV and IS from spiked human plasma were in the range of 91.7-93.4% and 80.2-84.1%, respectively. Stability of LEV in human plasma samples at different conditions showed that the drug was stable under the studied conditions. Matrix effect study showed a lack of matrix effect on mass ions of LEV and IS. The described method compared well with the commercial HPLC-UV method of Chromsystem (r(2)=0.99). The suitability of the developed method for therapeutic drug monitoring was demonstrated by measuring LEV in human plasma samples of epileptic patients treated with LEV.