ANALGESIC AND OTHER NEUROPHARMACOLOGIC EFFECTS OF PHENAZOCINE (NIH 7519, PRINADOL) COMPARED WITH MORPHINE

¹ Research and Development Division, Smith Kline & French Laboratories, Philadelphia, Pennsylvania

Some neuropharmacologic properties of phenazocine were compared to those of morphine in mice, rats, dogs and monkeys. In the rat, phenazocine was found to be approximately 25 times as potent as morphine (i.v. and s.c.) by the hot plate test and 15 times as potent as morphine (s.c.) by the tail withdrawal procedure. Orally, phenazocine was found to be only twice as potent as morphine as an analgesic (tail withdrawal method). Comparison of the tail withdrawal analgesic potency of morphine and phenazocine with their potencies by other procedures revealed, in general, similar quantitative separations in activity. For example, phenazocine was found to be approximately 12 times as potent as morphine in producing catalepsy, 10 times as potent in depressing spontaneous motor activity and 7 times as potent as morphine in blocking the conditioned escape response. Nalorphine effectively antagonized catalepsy induced by either morphine or phenazocine. Both morphine and phenazocine were effective antitussives in the dog, phenazocine being approximately equal in potency to morphine by this procedure. Overt effects produced by morphine and phenazocine in the mouse, rat, rabbit and dog were quite similar and were, in general, characterized by catalepsy and other signs of CNS depression. In the monkey, however, phenazocine produced either no overt effects or signs of CNS stimulation terminating in tonic-clonic convulsions, depending on the doses employed. Morphine, in contrast, caused characteristic depressant effects in this species.