Cimetidine and ranitidine: Comparison of effects on hepatic drug metabolism

Paired studies of hepatic microsomal function were conducted in eight subjects during treatment with two histamine H2antagonists, cimetidine and ranitidine. Cimetidine but not ranitidine inhibited the metabolism of antipyrine (phenazone) and demethylation of aminopyrine (aminophenazone) as measured by breath C02production after intravenous injection of C-amino-pyrine. These results suggest that the metabolic inhibitory actions on the liver may be separated from H2 antagonist effects, and that ranitidine has an advantage over cimetidine by not inhibiting microsomal drug oxidative function.