Simultaneous High Performance Liquid-Chromatographic Determination of Carbamazepine, Carbamazepine-10, 11-epoxide, Ethosuximide, Phenobarbital, Phenytoin, Primidone and Phenylethylmalonamide in Plasma

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Abstract
A common methodology is reported for the determination of 5 major anticonvulsants (carbamazepine, ethosuximide, phenobarbital, phenytoin and primidone) and their active metabolites (carbamazepine-10,11-epoxide and phenethylmalonamide) in 30 .mu.l of plasma. After a single step of deproteinization and extraction with acetonitrile, leading to an almost complete recovery of all the analytes, 5 .mu.l is injected on a reversed-phase column (Lichrosorb RP-18, 5 .mu.m). The anticonvulsants are eluted isocratically at a column temperature of 50.degree. C with a mobile phase consisting of acetonitrile/phosphate buffer pH 6.9 (40/60 by vol), and monitored at 208 nm. Quantitation, using peak height or peak area, is based on the ratio of analyte to internal standard (allylisobutylbarbital) referenced to a serum-based multiple drug standard. The composition and pH of the mobile phase, temperature of the column, choice of wavelength of detection and size of the column material are crucial for the optimal separation of these 5 drugs and their 2 active metabolites in a chromatographic time of only 12 min, without sacrificing high sensitivity and column life.