Simultaneous analysis of six antiepileptic drugs and two selected metabolites in human plasma by liquid chromatography after solid-phase extraction

A rapid and simple liquid chromatographic method with photodiode array detection was developed for the simultaneous determination of six antiepileptic drugs (oxcarbazepine, carbamazepine, lamotrigine, phenobarbital, primidone and phenytoin) and two metabolites (10, 11 -dihydro- 10-hydroxycarbamazepine and 10, 11 -dihydro-10-hydroxycarbamazepine, the main active metabolites of carbamazepine and oxcarbazepine, respectively) in human plasma. Separation of the analytes was achieved in less than 11.5 min on a C18 column (150 x 4.0mm, i.d. 4.5 mum) with a mobile phase composed of methanol, acetonitrile and a pH 3.0, 15 mM phosphate buffer containing 0.63% triethylamine (19.2:16.8:64.0, (v/v/v)), at 1 ml min(-1) flow rate. Two procedures were tested for the pretreatment of human plasma samples: protein precipitation with perchloric acid, and solid-phase extraction. The protein precipitation procedure did not allow for the analysis of 10, 1 1-dihydro-10, 11-epoxycarbamazepine. On the contrary, solid-phase extraction with hydrophilic-lipophilic balance cartridges gave good results in terms of extraction efficiency and reproducibility and allowed for the determination of all analytes. The HPLC-DAD method developed, coupled to a careful SPE procedure, seems to be suitable for the plasma level determination of simultaneously administered antiepileptic drugs. (C) 2002 Elsevier Science B.V. All rights reserved.