Rifampicin and vitamin D metabolism

Abstract
A 2 wk course of the enzyme inducing antibiotic rifampicin orally (600 mg/day) in 8 male [human] subjects resulted in a consistent fall in plasma 25-hydroxycholecalciferol (25-OHD) levels of around 70%, accompanied by increased oxidation of antipyrine and 6.beta.-hydroxycortisol (indicative of hepatic enzyme induction). Plasma levels of 1,25-dihydroxycholecalciferol, parathyroid hormone and calcitonin were not altered. The fall in 25-OHD may represent the earliest lesion of drug-induced osteomalacia.