Enantioselective determination of econazole in rat plasma and its application to a pharmacokinetic study

Econazole is a widely used chiral antifungal drug. In this paper, an enantioselective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for determination of econazole enantiomers in rat plasma for the first time. After addition of the internal standard (IS) clotrimazole, plasma samples were extracted by liquid-liquid extraction with n-hexane:2-propanol (98.5:1.5, v/v). Baseline separation of the enantiomers was achieved on a Chiralpak® IC column (250 mm × 4.6 mm, 5 μm) using acetonitrile-ammonium acetate buffer (5 mM) (85:15, v/v) as mobile phase. The detection of the analytes was performed in multiple reaction monitoring (MRM) mode with positive electrospray ionization. Transitions of m/z 381.07 → 124.92 and 276.78 → 164.92 were monitored for econazole enantiomers and clotrimazole, respectively. The linear range was 0.20-50.00 ng/mL with the lower limit of quantification of 0.20 ng/mL for both econazole enantiomers in plasma. The intra-day and inter-day precisions were not exceeding 10.2% and the accuracies were within ±15.0%. The validated method was successfully applied to the stereoselective pharmacokinetic study of econazole enantiomers in rat plasma after transdermal administration of racemic econazole nitrate cream. Significant differences were observed in C_max, AUC and CL/F of econazole enantiomers, indicating the enantioselective pharmacokinetic behavior of econazole in rats.