The antinociceptive effect of buprenorphine and its long-acting ester buprenorphine benzoate in rats.

Background: A long-acting analgesic is particularly desirable in patients with long-lasting pain. In order to prolong the duration of action of a potent analgesic, buprenorphine, a buprenorphine ester (buprenorphine benzoate) was synthesized in our laboratory. The aim of the study was to evaluate whether the ester form could have a long-lasting effect.
Methods: Two studies were carried out. In study 1, we evaluated the antinociceptive effect of buprenorphine HCI at dosage of 0.05, 0.1, and 0.6 micromol/kg. In study 2, we evaluated the antinociceptive effect of buprenorphine benzoate at dosage of 0.6 micromol/kg. Male Sprague-Dawley rats (n = 12 in each group of different treatment) were used and the antinociceptive effects of the testing compounds were evaluated using the plantar test (a thermal test).
Results: Intramuscular injection of buprenorphine HCI at dosage of 0.05, 0.1, and 0.6 micromol/kg in rats produced dose-related antinociceptive effects with duration of action of 3, 4, and 4 h, respectively. Intramuscular injection of buprenorphine benzoate at 0.6 micromol/kg produced a duration of action of 48 h.
Conclusions: Intramuscular injection of buprenorphine benzoate in rats produced a longer duration of action, which is 12-fold longer than that of buprenorphine HCI.