Biliary excretion of barbiturates.

1. Pentobarbitone and phenobarbitone are excreted into the bile of rats.2. The concentration of pentobarbitone and/or its metabolites in the bile is 22-fold higher than in the plasma; the concentration of phenobarbitone and/or its metabolites in bile is 10-fold higher than in the plasma.3. Probenecid decreases the excretion of the barbiturates into the bile.4. Twenty-eight per cent of a 35 mg/kg dose of pentobarbitone and 18% of a 75 mg/kg dose of phenobarbitone is excreted in the bile in 6 hours.5. Most of the pentobarbitone and phenobarbitone excreted into the bile is not in the form of the parent compound but rather as a more polar metabolite or metabolites.