Serum concentrations of buprenorphine after oral and parenteral administration in male mice.

Buprenorphine is the most commonly used drug for peri-operative pain relief in laboratory rodents. The systemic concentrations of buprenorphine were measured in mice following administration intravenously (i.v.), subcutaneously (s.c.), orally by gavage and by voluntary ingestion, to determine the post-administration serum concentration of buprenorphine. Voluntarily ingested buprenorphine resulted in long-lasting high serum concentrations, as did oral gavage administration (24 h serum concentration: 110 ng h/mL for both routes of administration). In contrast, buprenorphine administered parenterally remained in the circulation for a substantially shorter time (24 h serum concentration for i.v. and s.c. were 40 ng h/mL and 30 ng h/mL, respectively). This marked difference was probably due to the higher dose used for oral administration, which is regarded necessary for sufficient analgesic effect, and to the slower absorption of the oral boli, as well as saturation of the hepatic buprenorphine metabolising pathways. Voluntary ingestion of buprenorphine was found to constitute a practical way to provide laboratory mice with efficient pain relief.