A comparison of the analgesic effect of intramuscular nalbuphine and morphine in patients with postoperative pain.

In a double-study, using patients' subjective reports as indices of analgesia, the relative analgesic potency of intramuscular nalbuphine and morphine was determined in 56 postoperative patients. A total of 28 crossover comparisons (utilizing the twin passover, balanced four-point incomplete block design) were performed in two sequentially related experiments, each assay comparing 4 and 8 mg of morphine with either 3 and 6 or 6 and 12 mg of nalbuphine. When both intensity and duration of analgesia are considered (i.e., total analgesic effect), nalbuphine was 0.8 to 0.9 times as potent as morphine. In terms of peak analgesic effect, nalbuphine was 0.7 to 0.8 times as potent. Both the time-effect curves and the relative potency estimates suggest that nalbuphine has a slightly longer duration of action than morphine at doses that are equianalgesic in terms of peak effect. Side effects of the type usually noted after the administration of potent injectable analgesics to postoperative patients were observed after both morphine and nalbuphine. Although nalbuphine is a potent narcotic antagonist, no psychotomimetic reactions were observed.