Which enzyme is inhibited by the drug allopurinol, used to treat gout?

A Xanthine oxidase ✓
B Uricase
C Hypoxanthine-guanine phosphoribosyltransferase
D Adenosine deaminase

Explanation

Allopurinol is a xanthine oxidase inhibitor, which reduces the production of uric acid in the body and is used to treat gout.

Source

FDA Drug Label
Enzymes in Disease Pharmacology Purine Metabolism Disorders Easy MEDICAL Confidence: high