NEW METHOD FOR THE DETERMINATION OF 4 ANTIEPILEPTIC DRUGS IN HUMAN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

The concurrent administration of several antiepileptic drugs for the treatment of seizure disorders has become common practice. Lamotrigine is a new antiepileptic given in combination with other antiepileptic drugs, but which is not routinely measured in clinical laboratories. An isocratic high-performance liquid chromatographic method is described for the simultaneous measuring lamotrigine, carbamazepine, phenobarbital and phenytoin within 10 minutes. The chromatographic system used an Hichrom Spherisorb CN column (20 cm x 4 mm, i.d., 5 mum particle size), a muBondapak CN precolumn, and a mobile phase consisting of methanol : acetonitrile : 5 mM sodium acetate (5 : 20: 75: by volume, pH adjusted to 6.3 with acetic acid). BWA 725C was used as internal standard. The drugs were extracted from 200 mul of plasma with ethyl acetate, acetonitrile and 5 mM sodium acetate. After evaporation of the organic layer and reconstitution in mobile phase, 25 mul of extract was eluted with mobile phase at a flow rate of 1.2 ml/min. The eluted drugs were detected by their absorption at 205 nm and quantified from their peak heights. The method was found to be rapid, relatively simple to perform and sufficiently sensitive to determine each drug over its entire therapeutic range. Lower limits of detection varied from 50-100 ng/ml, absolute recoveries from 93-98 %, and mean intra- and inter-assay CVs were < 3.0 %.