Robust isocratic high performance liquid chromatographic method for simultaneous determination of seven antiepileptic drugs including lamotrigine, oxcarbazepine and zonisamide in serum after solid-phase extraction

A rapid, simple and robust method is presented for the simultaneous determination of seven antiepileptic drugs (AEDs), including primidone, phenobarbital, phenytoin, carbamazepine with its two major metabolites carbamazepine-10,11-epoxide and carbamazepine-10,11-(trans)-dihydrodiol and the new AEDs lamotrigine, hydroxycarbazepine (active metabolite of oxcarbazepine) and zonisamide in serum by high performance liquid chromatography (HPLC)-diode array detector (DAD). After solid-phase extraction, separation is achieved on an Alltima 3C18 analytical column using isocratic elution with a mixture of acetonitrile, methanol and phosphate buffer at 45 °C. The method is exhaustively validated, including experimental design in combination with statistical evaluation (ANOVA) to study the robustness of chromatography and sample preparation. Commonly co-administered antiepileptic drugs do not interfere with the method. Intra-day precision (RSD < 1.9%), linearity, lower limit of quantitation (LOQ < 0.065 mg/l) and robustness make the method suitable for daily therapeutic drug monitoring and pharmacokinetic studies.