Analgesic effect of intramuscular and oral nalbuphine in postoperative pain

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Abstract
In a double-blind study using patterns subjective reports as indices of analgesia, the relative analgesic potency of i.m. and oral nalbuphine was determined in 104 postoperative patients. Effects of single doses of 3 and 9 mg of i.m. nalbuphine were compared with those of 15- and 45-mg oral doses of nalbuphine using a parallel study design (26 patients/treatment group). When both intensity and duration of analgesia are considered (i.e., total analgesic effect), oral nalbuphine is 1/4 to 1/5 as potent as i.m. nalbuphine. In terms of peak effect oral nalbuphine is only 1/10 as potent. The oral/parenteral potency ratio for effect is close to those obtained by Houde in studies of morphine (1/6), metopon (1/5), hydromorphone (1/5) and oxymorphone (1/6) and suggests that oral nalbuphine undergoes substantial biotransformation on 1st pass through gut mucosa and liver. Since i.m. nalbuphine is approximately equipotent to morphine, it should be feasible to equal the analgesia induced by the usual i.m. doses of morphine with reasonable oral doses of nalbuphine. Nalbuphine is a mixed agonist/antagonist analgesic but no psychotomimetic reactions were observed.