Inhibition of uricase by pyrimidine and purine drugs

A number of barbiturates inhibit uricase from porcine liver competitively, the Ki, values being in the range 1 to 13 X 10(-3) mol/L. In general the Ki increases as the size of the substituents at C-5 increases. Theophylline also inhibits the enzyme competitively (Ki = 1 X 10(-3) mol/L) but theobromine and caffeine have no inhibitory action at 0.01 mol/L. A number of sulphonamides and some other heterocyclic compounds, at 10(-3) mol/L, do not inhibit uricase. The possible effects of such inhibition in clinical assays for plasma/serum urate are discussed but it is concluded that the compounds which were studied are unlikely to cause significant interference in the assay.