A chiral LC-MS/MS method for the stereospecific determination of efonidipine in human plasma.

Efonidipine hydrochloride is a new generation dihydropyridine Ca(2+) channel blocker designed to inhibit both T-type and L-type Ca(2+) channels. Efonidipine possesses a chiral carbon and is clinically administered as a racemate. In the present study, an enantioselective and sensitive LC-MS/MS method of determining efonidipine enantiomers in human plasma was developed and validated to characterize the stereoselective pharmacokinetics. Plasma samples were processed by liquid-liquid extraction (LLE). Chiral separation was optimized on a CHIRALPAK(®) ID column using an isocratic mobile phase of acetonitrile/water (60:40, v/v). Detection was using MS in multiple reaction monitoring (MRM) mode, using the transitions of m/z 632.3→91.1 for efonidipine enantiomers, and m/z 493.3→117.2 for cilnidipine (internal standard). The calibration curves were linear over 0.100-20.0 ng/mL for each enantiomer. The lower limit of quantification (LLOQ) for each enantiomer was established at 0.100 ng/mL. Intra- and inter-day precisions were less than 12.1% for each enantiomer in terms of relative standard deviation (RSD), and accuracies were between -5.0% and 5.0% in terms of relative error (RE) for each enantiomer. No chiral inversion was observed during sample storage, preparation procedure and analysis. The validated method was successfully applied to a stereoselective pharmacokinetic study of efonidipine in healthy subjects after oral administration of 40 mg (20 mg × 2) efonidipine hydrochloride tablets.

An LC-MS/MS method for simultaneous determination of cefprozil diastereomers in human plasma and its application for the bioequivalence study of two cefprozil tablets in healthy Chinese volunteers.

A rapid and sensitive liquid chromatography-tandem mass spectrometric method was developed for the first time and validated for the determination of cefprozil diastereomers in human plasma. The plasma samples were prepared by protein precipitation using acetonitrile. Detection was performed using an electronic spray ion source in the negative ion mode, operating in the multiple reaction monitoring of the transitions m/z 388.0 to m/z 205.0 for cefprozil diastereomers and m/z 346.1 to m/z 268.1 for cephalexin (the internal standard). The calibration curves of cis-cefprozil and trans-cefprozil were linear in the ranges 0.125-16.0 µg/mL and 0.0403-1.72 µg/mL, respectively. The lower limits of quantification of cis- and trans-cefprozil were 0.125 and 0.0403 µg/mL in human plasma, respectively. The intra- and inter-day precisions of cis- and trans-cefprozil were all <9.7%, and the accuracy ranged from 99.2 to 104.7% and from 100.6 to 102.2%, respectively. The validated method was successfully applied to a bioequivalence study of two cefprozil formulations in 24 healthy Chinese volunteers. The two cefprozil tablets were bioequivalent by measurement of cis-, trans- and total cefprozil. We suggest that the bioequivalence of cefprozil formulations can be evaluated only using cis-cefprozil as the analyte in future studies.

Determination of efonidipine in human plasma by LC-MS/MS for pharmacokinetic applications.

Efonidipine hydrochloride is a new generation dihydropyridine calcium channel blocker designed to inhibit both T-type and L-type calcium channels. For the first time, a simple and robust LC-MS/MS method was developed for the determination of efonidipine in human plasma over the range of 0.100-20.0ng/mL. Efonidipine was extracted from plasma by an LLE procedure, separated by LC and detected by MS/MS in positive mode ESI. The method was validated for selectivity, carryover, sensitivity, extraction recovery, matrix effects, linearity, accuracy and precision, dilution integrity and stability studies. The calibration curves were linear over 0.100-20.0ng/mL (r≥0.9980). The lower limit of quantification (LLOQ) was established at 0.100ng/mL. Intra- and inter-day precisions (LLOQ, low-QC, mid-QC, high-QC and ultra-high QC) were less than 12.5% in terms of relative standard deviation (RSD), and accuracies were between -5.0% and 5.0% in terms of relative error (RE). Matrix effect was acceptable (105.6-110.2%) and extraction recovery was reproducible (85.8-91.3%, RSD≤10.0%). Efonidipine was stable in the investigated conditions. The method was applied to the pharmacokinetics of efonidipine in human subject.

LC-MS/MS method for the determination of agomelatine in human plasma and its application to a pharmacokinetic study.

A sensitive and selective LC-MS/MS method for the determination of agomelatine in human plasma was developed and validated. After simple liquid-liquid extraction, the analytes were separated on a Zorbax SB-C18 column (150 × 2.1 mm i.d., 5 µm) with an isocratic mobile phase consisting of 5 mm ammonium acetate solution (containing 0.1% formic acid) and methanol (30:70, v/v) at a flow-rate of 0.3 mL/min. The MS acquisition was performed in multiple reaction monitoring mode with a positive electrospray ionization source. The mass transitions monitored were m/z 244.1 → 185.3 and m/z 285.2 → 193.2 for agomelatine and internal standard, respectively. The methods were validated for selectivity, carry-over, matrix effects, calibration curves, accuracy and precision, extraction recoveries, dilution integrity and stability. The validated method was successfully applied to a pharmacokinetic study of agomelatine in Chinese volunteers following a single oral dose of 25 mg agomelatine tablet.