Enzyme induction by phenobarbitone and vitamin K1 disposition in man.

The plasma disposition of an intravenous pharmacological dose of vitamin K1 was determined in seven healthy volunteers before and after chronic administration of phenobarbitone (100 mg nocte). Phenobarbitone produced a significant increase in antipyrine clearance and 6 beta-hydroxycortisol excretion in all volunteers, indicating induction of hepatic microsomal mixed-function oxidase enzymes. However, phenobarbitone administration had no effect on the plasma disposition of vitamin K1. We conclude therefore, that vitamin K1 is not metabolized to any significant extent, by phenobarbitone-inducible mixed-function oxidase enzymes.