Use of normal-phase microcolumn high-performance liquid chromatography for the study of hydrolytic stability, metabolic profiling and pharmacokinetics of an antiepileptic drug, benzonal.

A normal-phase microcolumn HPLC method is proposed for the quantitative determination of the most frequently used antiepileptic drugs and some compounds developed recently. The main advantage of this method, in comparison with other micro-scale HPLC techniques for antiepileptic drugs, is that it is used under isocratic conditions at room temperature (22 degrees C). The hydrolytic stability of benzonal (BZ) has been studied using this method together with mass spectrometry (MS), and IR, UV and NMR spectroscopy. Three pathways of hydrolytic degradation were established in alkaline conditions, whereas in an acid medium only one of these routes was followed. An investigation of the metabolic profiling of BZ in guinea-pigs showed that the drug undergoes fast hydrolysis in the intestinal tract forming phenobarbitone (PB) and benzoic acid (BA). Only PB was detected in brain tissue and it is probably responsible for the whole therapeutic effect. The pharmacokinetic parameters of this metabolite (PB) were determined in guinea-pigs, and their identity with the pharmacokinetic parameters of PB as the parent drug was confirmed.