Theobromine metabolism in man.

The effects of allopurinol on the plasma clearance and metabolism of theobromine have been investigated under multiple-dosing conditions. Allopurinol had no effect on the clearance of theobromine, indicating that the elimination of this compound is dependent on enzyme systems other than xanthine oxidase, presumably the hepatic mixed-function oxidases. The excretion of 3-methylxanthine, 6-amino-5-(N-methylformylamino)-1-methyluracil, and unchanged theobromine were similarly unaffected by the allopurinol treatment. Although allopurinol abolished the formation of 7-methyluric acid (7MU) and increased the excretion of 7-methylxanthine (7MX), the metabolic clearance to (7MX + 7MU) was not significantly different with and without allopurinol. It is proposed that the secondary biotransformation of 7MX to 7MU is mediated by xanthine oxidase.