Plasma renin concentration and phenobarbital levels in patients with epilepsy

Plasma renin activity, renin concentration, and renin substrate were measured in patients on long-term anticonvulsant medication. An inverse correlation was observed between phenobarbital levels and renin activity or concentration. There was a positive correlation between phenobarbital and renin substrate. Since elevation of renin substrate should have resulted in increased renin activity, it is possible that phenobarbital exerts 2 effects on the renin system: induction of renin substrate synthesis and suppression of renin release.