A long-acting analgesic is particularly desirable in patients with long-term pain. This study evaluates the antinociceptive effect and duration of action of a novel buprenorphine ester-buprenorphine pivalate-and shows whether this ester has a long-acting effect. The antinociceptive effects of buprenorphine HCl and pivalate were evaluated by using the plantar test in male Sprague-Dawley rats. We found that intramuscular injection of buprenorphine HCl 0.03, 0.1, and 0.3µmol/kg in rats produced dose-related antinociceptive effects of 2, 3, and 4h, respectively. Intramuscular injection of buprenorphine pivalate 0.3, 3, and 30µmol/kg also produced dose-related antinociceptive effects, but with longer durations of action of 48, 52 and 54h. Under an equi-molar basis of 0.3µmol/kg, the durations of action of intramuscular buprenorphine HCl and buprenorphine pivalate were 4 and 48h, respectively. We conclude that intramuscular injection of buprenorphine pivalate produced a long-lasting antinociceptive effect which was much longer (12-fold) than intramuscular buprenorphine HCl.
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Kao et al. (2005) studied this question.
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