Simultaneous Determination of Primidone and Its Active Metabolites in Rat Plasma by High-Performance Liquid Chromatography Using a Solid-Phase Extraction Technique

Abstract

Primidone (PRM) and its active metabolites, phenylethylmalonamide (PEMA) and phenobarbital (PB), in rat plasma were simultaneously determined using a solid‐phase extraction technique followed by high‐performance liquid chromatography (HPLC). Twenty microliters of plasma was applied to a Bond‐Elut C‐18 cartridge column with 0.1 μg of acetanilide (internal standard, IS). After the column was washed, PRM, PEMA, PB, and IS were eluted with methanol and injected into the HPLC system. Calibrations for these substances were linear in the range of 0–20 μg/mL. The coefficients of variation were 1.5–7.9% and 3.4–9.1% in the within‐day and between‐day assays, respectively. The recovery rates were 96.8–101.8%. The pharmacokinetics of these substances were examined after oral administration of PRM (50 mg/kg) to rats. TheTmaxvalues for PRM, PEMA, and PB were 1.4, 5.7, and 6.6 h, respectively, and theCmaxvalues were 18.2, 8.1, and 9.6 μg/mL, respectively. This method is useful for pharmacokinetic studies of PRM and its active metabolites.