METABOLIC DISPOSITION OF C-14 VENLAFAXINE IN MOUSE, RAT, DOG, RHESUS-MONKEY AND MAN

1. The metabolic disposition of venlafaxine has been studied in mouse, rat, dog, rhesus monkey and man after oral doses (22, 22, 2, and 10 mg/kg, and 50 mg, respectively) of C-14-venlafaxine as the hydrochloride. 2. In all species, over 85% of the administered radioactivity was recovered in the urine within 72 h, indicating extensive absorption from the GI tract and renal excretion. 3. Venlafaxine was extensively metabolized, with only 13.0, 1-8, 7-9, 0.3 and 4.7% dose appearing as parent compound in urine of mouse, rat, dog, monkey and man, respectively. The metabolite profile varied significantly among species, but primary metabolic reactions were demethylations and the conjugation of phase I metabolites. Hydroxylation of the cyclohexyl ring also occurred in mouse, rat and monkey, and a cyclic product was formed in rat and monkey. Glucuronidation was the primary conjugation reaction, although sulphate conjugates were also detected in mouse urine. 4. While no metabolite constituted more than 20% dose in any species except man, the major urinary metabolites were: mouse, N,O-didesmethyl-venlafaxine glucuronide; rat, cis-1,4-dihydroxy-venlafaxine; dog, O-desmethyl-venlafaxine glucuronide; monkey, N,N,O-tridesmethyl-venlafaxine; and man, O-desmethyl-venlafaxine.