Thiopurinol: dose-related effect on urinary oxypurine excretion

1. The important fact which emerges from these studies both without and with dietary purine supplementation is that thiopurinol dose possess apparent in vivo xanthine oxidase inhibitory activity but the dose must be increased well above therapeutic levels for this effect to manifest. 2. The considerable reduction in total endogenous urinary purine excretion at these high doses substantiates an additional inhibitory effect of thiopurinol on de novo purine synthesis. 3. Thiopurinol, like its analogue allopurinol, is also capable of reducing the absorption of dietary purine administered in the form of guanine in the pig.