Antinociceptive activity of pentamorphone, a 14-beta-aminomorphinone derivative, compared to fentanyl and morphine

The analgesic potency of pentamorphone, a 14-beta-aminomorphinone derivative, was compared to that of fentanyl and morphine by examining quantal dose-effect curves generated from data obtained in the mouse hot plate, rabbit tooth-pulp, and dog tail clamp tests. Onset and duration of antinociceptive effects were also compared. The ED50 values (mg/kg) were determined in mice for pentamorphone (0.0039), fentanyl (0.016), and morphine (7.3). In the rabbit tooth pulp test the ED50 values were 0.0009 mg/kg for pentamorphone, 0.0074 mg/kg for fentanyl, and 1.1 mg/kg for morphine; in the dog tail clamp test these values were 0.012 mg/kg for pentamorphone and 0.018 mg/kg for fentanyl. Duration of action (defined as the time until response to tooth pulp stimulation declined to 50% of maximum possible effect [MPE]) was 10 min with twice the IV ED50 for pentamorphone in mice. This duration was similar to that of the equipotent dose of fentanyl but much shorter than the duration of an equipotent potent dose of morphine (60 min). The duration in rabbits of the ED98 (IV) dose of pentamorphone was 65 min compared to 35 min for an equipotent dose of fentanyl and 200 min for morphine. Intramuscular doses of pentamorphone had significantly faster onset and shorter duration times than equipotent doses of morphine in both mice and rabbits. Pretreatment with naloxone in mice and rabbits attenuated the development of the antinociceptive effects of pentamorphone. This study shows that pentamorphone is a potent analgesic with a duration of action similar to that of fentanyl.