Progabide-induced changes in carbamazepine metabolism

Carbamazepine (CBZ) and carbamazepine 10,11 epoxide (CBZ-E) concentrations were measured during a safety and efficacy trial of progabide. The average CBZ and CBZ-E serum concentrations were calculated from serial measurements during placebo and active treatment periods. Significant decreases in CBZ and significant increases in CBZ-E were observed after the first dose of progabide, and these changes persisted during 3 months of active treatment. Ninety-five percent of the patients had increases in the epoxide/CBZ ratio at the end of 3 months of treatment. These changes are consistent with displacement of CBZ from protein binding sites and inhibition of CBZ-E metabolism induced by progabide and are analagous to the interaction between valproate and CBZ.