Physiologic disposition of nabilone, a cannabinol derivative, in man

Abstract

Nabilone is a cannabinoid that is being evaluated in man as a potentially useful psychoactive drug. We found that nabilone was readily absorbed from the human gastrointestinal tract when administered orally as a coprecipitate with polyvinyl-pyrrolidone. The absorbed drug disappeared from plasma rather rapidly (half-life, approximately 2 hr), evidently due to extensive tissue distribution and rapid metabolism. The metabolites of nabilone persist in plasma for extended periods (half-life of total radioactivity exceeds 20 hr). Circulating metabolites include isomeric carbinols formed by reduction of the ketone in the 9-position of nabilone. Nabilone is eliminated in feces (about 65% of dose) and urine (20%). The excretory products in urine have not been identified, but metabolites that are labile to hydrolysis by beta-glucuronidase or sulfatase do not appear to be formed in significant amounts. A metabolite of nabilone in feces has been identified as a diol formed by reduction of the 9-keto group plus oxidation at the penultimate carbon of the dimethylheptyl side chain. The long duration of action of nabilone in the face of rapid and extensive metabolic elimination suggests that the pharmacologic effects, at least in part, may be exerted by one or more active metabolites.