Meptazinol is an agonist-
antagonist opioid analgesic believed to be unique in its selectivity for mu1 (high affinity) receptors and its
cholinergic activity. Our objectives were to determine the relative
analgesic potency of intramuscular
meptazinol and
morphine and to compare mood and side effects in 102 patients with
cancer who have
postoperative pain.
Meptazinol (50, 100, and 200 mg) and
morphine (4, 8, and 16 mg) were given for moderate to severe
pain in a double-blind, randomized but balanced, incomplete block design. Serial multiple assessments of
pain, relief, mood, and side effects were made. The most precise estimates of relative
analgesic potency indicate that
meptazinol is equivalent to 10 mg
morphine at 120 mg (95% confidence interval 80 to 170 mg) for peak effect and at 175 mg (95% confidence interval 125 to 270 mg) for total effect. Mean (+/- SE) times to peak effect and to remedication were 0.9 +/- 0.1 and 3.6 +/- 0.2 hours for
meptazinol and 1.4 +/- 0.1 and 4.8 +/- 0.4 hours for
morphine at equianalgesic peak effects. The percentages of subjects with one or more side effects were 18, 49, and 73 for graded
meptazinol doses and 32, 49, and 65 for graded
morphine doses. Mean numbers of side effects per subject were 0.3, 1.5, and 3.5 for
meptazinol and 0.5, 0.7, and 1.7 for
morphine. Profiles of side effects differed. Mood improvement and overall satisfaction were dose related and greater for
morphine than for
meptazinol. Side effects may limit the use of
meptazinol in doses that relieve severe
postoperative pain.