This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Which of following drug inhibits xanthine oxidase: September 2007 
Select and explain. 
A. Probenicid, B. Quiniarcine, C. Allopurinol, D. Sulfinpyrazone
C: Allopurinol
Answer: C: Allopurinol 
Explanation: Ans. C: Allopurinol Xanthine oxidase is involved in purine metabolism. Inhibition of xanthine oxidase reduces the production of uric acid, and several medications that inhibit xanthine oxidase are indicated for treatment of hyperuricemia and related medical conditions including gout. Xanthine oxidase inhibitors are: a. Purine analogues include allopurinol, oxypurinol, and tisopurine. b. Others include febuxostat and inositols (phytic acid and myo-inositol).