Studies on the chiral separation of pheniramine and its enantioselective pharmacokinetics in rat plasma by HPLC-MS/MS

As a highly potent first-generation histamine H-1-receptor antagonist, pheniramine is a chiral drug and consists of a pair of enantiomers. In this study, a sensitive and enantioselective HPLC-MS/MS method has been developed for the determination of pheniramine enantiomers in rat plasma for the first time. The enantioseparation was performed on a Chiralpak AGP column with 10 mM ammonium acetate buffer (pH 4.5) as mobile phase. Chlorpheniramine was selected as the internal standard. Both pheniramine and internal standard were detected by mass spectrometry in multiple reaction monitoring mode (MRM) with a positive electrospray ionization source. Transitions of m/z 240.97 -> 195.84 and 275.21 -> 229.85 were monitored for pheniramine and chlorpheniramine, respectively. The method was validated over the concentration range of 1-400 ng/mL for each pheniramine enantiomer and the lower limit of quantification was 1 ng/mL. The relative standard deviations of the infra-day and inter-day precision were not greater than 11.7%, and relative errors of the accuracy ranged from -3.3% to 1.7%. Finally, the proposed method was applied to the enantioselective pharmacokinetic study of pheniramine enantiomers after oral administration of 20 mg/kg racemic pheniramine to Wistar rats. It was found that the maximum plasma concentration (C-max), area under the concentration-time curve (AUC), and clearance of S-pheniramine were higher than those of R-pheniramine.