<prompt> Which of the following describes the action of allopurinolInhibits metabolism of purines to uric acidInterferes with cytokine productionInhibits uric acid reabsorptionInhibits prostaglandin biosynthesis  <response>: URIC ACID SYNTHESIS INHIBITORS Allopurinol:- Mech of action:- Allopurinol is a sho-acting t 12 2 hrs competitive inhibitor of xanthine oxidase, but its major metabolite alloxanthine oxypurine is a long-acting t 12 24 hrs and noncompetitive inhibitor--primarily responsible for uric acid synthesis inhibition in vivo. At high concentrations, allopurinol also becomes noncompetitive inhibitor. During allopurinol administration, plasma concen tration of uric acid is reduced and that of hypoxanthine and xanthine is somewhat increased. Because of raised levels of xanthine and hypoxanthine, some feedback inhibition of de novo purine synthesis and reutilization of metabolically derived purine also occurs. Ref:- kd tripathi; pg num:-216 