Twin crossover relative potency analgesic assays in man. II. Morphine vs. 8-methoxycyclazocine.

Using the twin crossover, balanced incomplete block design described in the previous paper, a double-blind determination of the relative analgesic potency of graded intramuscular doses of Win 20,836 (8-methoxycyclazocine) and morphine was carried out in patients with postoperative pain. Although no preliminary data at all on the human analgesic activity of Win 20,836 were available, the sequential decision-making process designed to choose the doses of the test medication most closely equianalgesic with the standard functioned efficiently to establish doses of Win 20,836 that had analgesic activity. Unfortunately, the occurrence of psychotomimetic side effects prevented the administration of doses of Win 20,836 equieffective with the morphine standard, and this necessitated substantal extrapolation of the dose-response curve of the test drug to arrive at a relative potency estimate. However, our relative potency estimate, which indicated that Win 20,836 is three to six times as potent as morphine, was dependable enough to predict with reasonable certainty that doses of Win 20,836 equieffective to the usual doses of morphine would produce an unacceptable level of psychotomimetic side effects. Clinical investigation of the drug was therefore terminated.