Effects of cirrhosis and ageing on the elimination and bioavailability of ranitidine.

The plasma concentrations of ranitidine after oral and intravenous administration have been measured in 10 healthy young adults, nine cirrhotic patients, and eight healthy elderly people. In the first of these bioavailability was 51 +/- 4% and half life 161 +/- 11 minutes after oral and 124 +/- 5 minutes after intravenous administration. In the cirrhotics bioavailability was increased to 70 +/- 7%, clearance was reduced, and there was a modest increase in half life. In the elderly bioavailability was similar to that in young adults, clearance was markedly reduced, and half life was prolonged to 241 +/- 7 minutes after oral and 194 +/- 11 minutes after intravenous administration. It is predicted that blood levels in cirrhotics and the elderly would be 50 to 60% higher than in healthy young adults after repeated oral administration of similar doses.