Differential kinetics of cinromide and two of its metabolites in epileptic patients

Cinromide is an experimental anticonvulsant currently in phase II testing. A single oral dose (900 mg) of cinromide was administered to 8 epileptic subjects on phenytoin therapy. Plasma samples drawn during the next 36 h were analyzed for cinromide and its amide and acid metabolites. The absorption rate of cinromide varied widely between subjects producing maximum cinromide concentrations between 0.5 and 2.5 h after the dose. The median elimination half lives of cinromide and the amide and acid metabolites were 0.73, 1.65, and 4.85 h respectively. The oral clearance of cinromide (median = 135 l/h) suggests that it is subject to first pass metabolism. In all subjects the area under the curve (AUC) of acid metabolite (632 to 1777 microM/l) was greater than the AUC of amide metabolite (77 to 185 microM/l) which was greater than the AUC of cinromide (5 to 89 microM/l). Steady-state concentration ratios of metabolite to parent drug predicted from the AUC data were 3.8 for the amide and 35.8 for the acid metabolite. The amide metabolite is known to have anticonvulsant properties and, until the relative contributions of metabolites and parent drug to the efficacy of cinromide are resolved, the monitoring of metabolites as well as parent drug is imperative.