EFFECT OF CYPRENORPHINE (M285), A MORPHINE ANTAGONIST, ON THE DISTRIBUTION AND EXCRETION OF ETORPHINE (M99), A POTENT MORPHINE-LIKE DRUG

¹ Radioisotope Unit, Pharmaceutical Research Laboratories, Reckitt & Sons Ltd., Kingston-upon-Hull, England

The distribution and excretion of tritium-labeled etorphine (a morphine-like drug of unprecedented potency) in the rat have been studied. The changes in this distribution brought about by the administration of nonradioactive cyprenorphine (a morphine antagonist) injected conjointly have also been investigated. The major route of excretion of radioactivity is in the feces. Cyprenorphine increases the rate of secretion of the labeled drug (in the bile) into the duodenum and its speed of propulsion through the intestine. The concentration of etorphine equivalents in nervous tissue is reduced by the cyprenorphine.