Abstract

Nineteen narcotic antagonists and morphine were measured for their potency in inhibiting phenylquinone-induced writhing in mice and in antagonizing the activity of meperidine on the tail-flick test in rats. Cyclorphan and cyclazocine were more potent than morphine in producing a decrease in writhing; pentazocine and its C-9 ethyl homolog were less potent than morphine; naloxone was inactive. Of the pairs of optical isomers, the l-isomers of cyclazocine and pentazocine were more potent than their d-isomers. Among the pairs of geometrical isomers, the cis-isomer of cyclazocine was more potent than the trans-isomer, whereas the trans-isomer of pentazocine was more potent than the cis-isomer. The estimated potency of the drugs in decreasing writing was unrelated to their estimated potency as narcotic antagonists, but seemed to correlate roughly with their estimated potency as analgesics in man.