Twin Crossover Relative Potency Analgesic Assays in Man. II. Morphine Vs. 8‐Methoxycyclazocine

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Abstract
Using the twin crossover, balanced incomplete block design, a double-blind determination of the relative analgesic potency of graded i.m. doses of Win 20,836 (8-methoxycyclazocine) and morphine was carried out in patients with postoperative pain. The occurrence of psychotomimetic side-effects prevented the administration of Win 20,836 equieffective with the morphine standard and this necessitated substantial extrapolation of the dose-response curve of the test drug to arrive at a relative potency estimate. The relative potency estimate, which indicated that Win 20,836 is 3-6 times as potent as morphine, was dependable enough to predict that Win 20,836 doses equieffective to the usual morphine doses would produce an unacceptable level of psychotomimetic side-effects.