Enantioselective HPLC determination and pharmacokinetic study of secnidazole enantiomers in rats

• The first chiral HPLC method for detecting secnidazole in biological samples.
• Baseline resolution was achieved on a Chiral-AGP column within 7.0 min.
• The method was validated and applied to a pharmacokinetic study in rats.
• The disposition of secnidazole is not significantly stereoselective in rats.
• Chiral inversion and enantiomer–enantiomer interaction do not occur in rats.

Secnidazole is a long-lasting nitroimidazole antimicrobial agent that is used as racemic mixture in clinical settings. We developed and validated an enantioselective high-performance liquid chromatography method to determine secnidazole enantiomers in rat plasma. Secnidazole enantiomers and S-(−)-ornidazole (internal standard) were extracted from 50 μL of rat plasma using diethyl ether–dichloromethane (3:2, v/v). Baseline resolution (Rs = 2.45) was achieved within 7.0 min on a Chiral-AGP column (150 mm × 4.0 mm, 5 μm) at 20 °C. The mobile phase consisted of 10 mM ammonium acetate–methanol (96:4, v/v) and was delivered at a flow rate of 0.5 mL/min with ultraviolet detection at 318 nm. The method was linear over the concentration range 0.500–100 μg/mL for both enantiomers. The lower limit of quantification was 0.500 μg/mL for both enantiomers. The relative standard deviation values for intra- and inter-day precision were 0.8–8.6 and 1.8–8.2% for S-(+)-secnidazole and R-(−)-secnidazole, respectively. The relative error values of accuracy ranged from −7.8 to 1.1% for S-(+)-secnidazole and from −7.3 to −0.1% for R-(−)-secnidazole. The method was successfully used to determine the pharmacokinetic properties of secnidazole enantiomers in rats after administration of the racemate and individual enantiomers. The pharmacokinetic results indicate that the disposition of secnidazole enantiomers is not stereoselective and chiral inversion and enantiomer–enantiomer interaction do not occur in rats.