Excretion and metabolism of intramuscularly administered [14C]-haloperidol decanoate in rats

Urinary, fecal and biliary excretion, together with enterohepatic circulation, of radioactivity were studied after intravenous (50 mg eq/kg) and intramuscular (5 and 50 mg eq/kg) administration of [14C]-haloperidol decanoate in rats. The composition of urinary and biliary metabolites was also examined. The rate of excretion after intravenous administration lowered rapidly with the half-life of about 1.5 days and about 95% of dose was excreted in excreta within 10 days. Shortly after intramuscular administration, the rate of excretion lowered rapidly but then more gradually later (half-lives after administration of 5 and 50 mg eq/kg were 16.4 and 11.2 days, respectively). About 90% of dose was excreted within 42 days after intramuscular administration. About 1.6% of dose/day was excreted in the bile during 15-17 days after intramuscular administration, of which about 30% was reabsorbed within 24 h (enterohepatic circulation). The major urinary metabolite was p-fluorophenylaceturic acid and the biliary metabolite, glucuronide and sulfate of haloperidol. No unchanged decanoate was detected in the excreta.