Allopurinol acts by -

Ans. is 'a' i.e., Inhibiting synthesis of uric acid Allopurinolo It is hypoxanthine analogueo It is a uric acid synthesis inhibitor.o It is a substrate as well as inhibitor of xanthine oxidase.o Allopurinol itself is a short acting (t 1/2 - 2 hours) competitive inhibitor of xanthine oxidase, but its major metabolite alloxanthine (oxypurine) is a long acting (t 1/2 - 24 hours) noncompetitive inhibitor - primarily responsible for uric acid synthesis inhibition.o During allopurinol therapy concentration of hypoxanthine and xanthine increases, while uric acid decreases - All three are excreted in urine.o Since xanthine and hypoxanthines are more soluble and have a higher renal clearance than uric acid, precipitation and crystallization in urine and tissues does not occur.o Allopurinol is the first choice drug in chronic gout. It can be used in both over producers and under excretors of uric acid.o It is also used in secondary hyperuricemia, to potentiate 6-mercaptopurine or azathioprine.o Hypersensitivity reaction (rashes, fever, malaise) is the most common adverse effect.