Adverse Effects of Phenobarbital on Corticosteroid Metabolism in Patients with Bronchial Asthma

Abstract
The effects of phenobarbital therapy on plasma kinetics of labeled dexamethasone were investigated in 11 asthmatic patients. Phenobarbital caused a mean decrease in half-life of 117 minutes (-44 per cent) and an increase in metabolic clearance rate of 272 liters per day (+88 per cent). Urinary radioactivity excretion rate rose, the greatest increase occurring in the unconjugated ethyl acetate fraction. Increased urinary 6-hydroxycortisol excretion supported the presence of hepatic enzyme induction. These effects were not noted in five placebo-treated patients.