Metabolism of Drugs. LXIX. Studies on the Urinary Metabolites of Morphine in Several Mammalian Species

Abstract

In the previous study of this series, morphine was shown to be metabolized not only to morphine-3-glucuronide, but also to morphine-6-glucuronide in rabbits. The present study have demonstrated that this is common in rabbits, guinea pigs, rats, mice and human. As a minor metabolite of morphine, normorphine was also detected in the urine samples of these species by thin-layer chromatography. However, the excretion of this metabolite into the urine of guinea pigs given morphine was not conclusive, since the similar spot was also observed on the thin-layer chromatogram of the urine extract from untreated animals. Quantitative estimation of major metabolites of morphine in the urine of rabbits and guinea pigs indicated that most of the dose was accounted for as conjugated morphine, but in rats morphine was excreted mostly as free morphine and in lesser amount as the conjugates in 24 hr urine.