Binding of anticonvulsant drugs to cytochrome P-450: correlation with evidence of induction of hepatic microsomal enzymes

Mephenytoin, diphenylhydantoin, pheneturide, and phenobarbital produced a concentration-dependent inhibition in the binding of hexobarbital to cytochrome P-450 at the type 1 site, while sulthiame slightly potentiated, and ethosuximide did not affect the binding characteristic of hexobarbital. Diphenylhydantoin, phenobarbital, and pheneturide have previously been shown to enhance the urinary excretion of D-glucaric acid (DGA), while sulthiame inhibited the potentiation of DGA excretion caused by these drugs, and ethosuximide produced no change. The results suggest a close relationship between the ability of these drugs to induce hepatic microsomal drug-metabolizing enzyme systems (as indicated by enhancement of DGA excretion) and binding behaviour at the type 1 site.