Isocratic Reversed-Phase HPLC for Simultaneous Separation and Determination of Seven Antiepileptic Drugs and Two of their Active Metabolites in Human Plasma

A simple reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of the antiepileptic drugs (AEDs) zonisamide (ZNS), primidone (PRI), lamotrigine (LTG), phenobarbital (PB), phenytoin (PHT), oxcarbazepine (OXC), and carbamazepine (CBZ) and two of their active metabolites, monohydroxycarbamazepine (MHD) and carbamazepine 10,11-epoxide (CBZE) in human plasma. Plasma (100 μL) was pretreated by deproteinization with 300 μL methanol containing 20 μg mL⁻¹ propranolol hydrochloride as internal standard. HPLC was performed on a C₈ column (4.6 mm × 250 mm; particle size 5 μm) with methanol–acetonitrile–0.1% trifluoroacetic acid, 235:120:645 (v/v), as mobile phase at a flow rate of 1.5 mL min⁻¹. ZNS, OXC, and CBZ were monitored by UV detection at 235 nm, and PRI, LTG, MHD, PB, PHT, and CBZE by UV detection at 215 nm. Relationships between response and concentration were linear over the concentration ranges 1–80 μg mL⁻¹ for ZNS, 5–50 μg mL⁻¹ for PRI, 1–25 μg mL⁻¹ for LTG, 1–50 μg mL⁻¹ for MHD, 5–100 μg mL⁻¹ for PB, 1–10 μg mL⁻¹ for CBZE, 0.5–25 μg mL⁻¹ for OXC, 1–50 μg mL⁻¹ for PHT, and 1–25 μg mL⁻¹ for CBZ. Intra-day and inter-day reproducibility were adequate (coefficients of variation were ≤11.6%) and absolute recovery ranged from 95.2 ± 6.13 to 107.7 ± 7.76% for all the analytes; for the IS recovery was 98.69 ± 1.12%. The method was proved to be accurate, reproducible, convenient, and suitable for therapeutic monitoring of the nine analytes.