Application of capillary electrophoresis coupled to laser-induced fluorescence detection for the selective determination of vigabatrin in human plasma

Vigabatrin (4-amino-5-hexenoic acid) is an antiepileptic drug whose probable mechanism of action is the inhibition of GABA transaminase, which leads to reduced neuronal activity as a consequence of the increased GABA concentration. The drug is orally administered at doses ranging from 1.5 to 4 g/day and the commonly reported therapeutic plasma concentrations are between 20 and 60 g/mL. Side effects such as fatigue, drowsiness, headache and weight gain are frequent, but also irreversible visual field defects may occur in long-term treated patients. In order to accurately and selectively determine Vigabatrin plasma levels in patients under treatment with the drug, a capillary electrophoretic method with laser-induced fluorescence (LIF) detection (laser wavelength 488 nm) has been developed. Sample pre-treatment is based on SPE with mixed-mode lipophilic-strong cation exchange (MCX) cartridges, that allowed the removal of interference and good extraction yield (>96%). Since the analyte is neither fluorescent nor UV-active, a fast (30 min) derivatisation procedure with 6-carboxyfluorescein-N-succinimidyl ester has been developed, allowing the selective determination of Vigabatrin by LIF. The BGE is composed of a pH 9 borate buffer, supplemented with N-methylglucamine in order to separate the analyte from labelling agent excess peaks. Good linearity was found over the 10-120 µg/mL concentration range. The method shows good precision (RSD%< 6.7). Finally, the method has been applied to the determination of the analyte in real plasma samples from patients undergoing treatment with Vigabatrin; accuracy assays gave all results between 97.0 and 101.6%. Thus, the method seems to be suitable for the therapeutic drug monitoring of Vigabatrin in epileptic patients.