Biotransformation of oxaprotiline: isolation and identification of metabolites in urine of rat and dog.

The biotransformation of oxaprotiline has been investigated in rat and dog after oral administration of racemic 14C-labelled oxaprotiline X HCl. Rats excreted 28% dose in urine within 120 h and dogs 32% within 96 h. The metabolites were isolated by liquid chromatography and their structures elucidated by spectroscopic methods. In both species, oxaprotiline is extensively metabolized. Principal metabolic transformations are aromatic hydroxylations and formation of aromatic hydroxy-methoxy derivatives, N-demethylation, deamination and direct O-glucuronidation. Most of the primary metabolites formed by functionalization reactions occur in both free and glucuronidated form. In the rat, diastereoisomeric 3-hydroxy metabolites and the corresponding phenolic glucuronides are predominant. Products of deamination are minor, and products of direct O-glucuronidation are not detectable. In the dog, biotransformation is more complex. Major metabolites are diastereoisomeric 2- and 3-hydroxy compounds and the corresponding phenolic glucuronides. Oxidations in the side-chain and direct O-glucuronidation are minor metabolic pathways.