Background: A long-acting analgesic may be particularly desirable in patients with long-lasting pain. In order to provide a long-acting analgesic effect, a novel buprenorphine ester, buprenorphine palmitate, was synthesized in our laboratory. The aim of the study was to evaluate whether the ester had a long-lasting effect.
Methods: The antinociceptive effects (dose-range studies) of buprenorphine HCl and buprenorphine palmitate were evaluated using the plantar test in Sprague-Dawley rats.
Results: We found that intramuscular injection of buprenorphine HCl 0.05, 0.1 and 1 micromol/kg in rats produced dose-related antinociceptive effects of 2, 3, and 4 h, respectively. Intramuscular injection of buprenorphine palmitate 1, 5, and 10 micromol/kg also produced dose-related antinociceptive effects of 72, 76 and 78 h, respectively. On an equimolar basis of 1 micromol/kg, the durations of action of intramuscular buprenorphine HCl and buprenorphine palmitate were 4 and 72 h, respectively.
Conclusions: Intramuscular injection of buprenorphine palmitate in rats produced a long-lasting antinociceptive effect which was much longer (18-fold) than did intramuscular buprenorphine HCl.