Biliary excretion of H2-receptor antagonists

The biliary excretion of ranitidine and famotidine has been studied using percutaneous biliary drainage in patients with complete extrahepatic biliary obstruction due to pancreatic carcinoma. Following 50 mg ranitidine i.v. 0.7 to 2.6% of the dose was recovered in bile collected over 24 h. At steady state (300 mg ranitidine/d po) a similar amount (0.3 to 1.0% of daily dose) was excreted by this route (n = 3). Following single i.v. (20 mg) and oral (40 mg) doses of famotidine (n = 2), even lower percentages (0.1% and 0.4%, respectively) were recovered in the 24 h bile. This negligible biliary excretion cannot account for the so-called second peak phenomenon observed in some individuals following a single dose of an H2-receptor antagonist.