The systemic bioavailability of buprenorphine by various routes of administration.

The systemic bioavailability of buprenorphine has been studied in female rats following single doses (200 microgram kg-1) administered by one of six different routes. Relative to the 100% bioavailability from the intraarterial route the mean bioavailabilities were intravenous, 98%; intrarectal, 54%; intrahepatoportal, 49%; sublingual, 13%; and intraduodenal, 9.7%. Area under the curve analysis of buprenorphine concentrations in blood showed the relative fractions of drug extracted (first pass) by gut, liver and lung to be 0.80, 0.50 and 0.02 respectively, In situ absorption studies showed that the poor availability of intraduodenally administered buprenorphine is not due to slow or incomplete absorption.