Comparison of the analgesic effects of intravenous nalbuphine and pentazocine in patients with postoperative pain.

One hundred patients, who were in pain during the immediate postoperative period after upper abdominal operations, were included in this double-blind, between-patient, two-dose study. During N2O-O2-halothane-relaxant anaesthesia no analgesics were given. The patients received 0.07 mg/kg or 0.14 mg/kg of nalbuphine or 0.3 mg/kg or 0.6 mg/kg of pentazocine by intravenous injection. Pain and side effects were assessed for 4 h after administration of the test drug, or until the pain returned to the pre-injection level, when a conventional analgesic was given. The onset of pain relief was similar and the peak effect occurred about half an hour after the injection after both drugs. On a milligram basis, nalbuphine seemed to be about three times as potent as pentazocine. The duration of action seemed to be slightly longer after nalbuphine, but 2 1/2 hrs. after the injection the pain had returned to preinjection level in 2/3 of the patients, even after the higher doses of both drugs. Except for sleepiness, there were few side effects and they were similar after both drugs. No psychotomimetic effects were observed.