Isolation of a novel morphinan 3-O-diglucuronide metabolite from dog urine

Following oral administration of the narcotic antagonist nalmefene [17-(cyclopropylmethyl)-4,5 alpha-epoxy-6-methylenemorphinan-3,14-diol] labeled with 14C to the dog, approximately 50% of the dose was excreted in the urine as a highly polar water-soluble conjugate. Although this major metabolite could be hydrolyzed with beta-glucuronidase to yield nalmefene, the intact conjugate was chromatographically more polar on reversed-phase high-performance liquid chromatography (HPLC) than authentic nalmefene 3-O-glucuronide. Milligram quantities of the metabolite were subsequently isolated and subjected to fast atom bombardment (FAB) mass spectral and nuclear magnetic resonance (NMR) analyses. The conjugate was identified as nalmefene 3-O-beta-diglucuronide with a 1,2-beta linkage between the two glucuronic acids. It is unlikely that this novel form of conjugate is unique to nalmefene and it is probably a metabolite of other morphinans and/or similar drugs in the dog. Nalmefene 3-O-diglucuronide is not a metabolite of nalmefene in man.