Which of the following drugs is a correct illustration of how drug development has exploited the inhibition of drug metabolism? A. Allopurinol B. Isoniazid C. Warfarin D. Erythromycin

Allopurinol is a drug used to treat gout and kidney stones by reducing high blood uric acid levels. It acts as a suicide inhibitor of the enzyme xanthine oxidase.

Xanthine oxidase is an enzyme responsible for the metabolism of hypoxanthine to xanthine, and then xanthine to uric acid. By inhibiting xanthine oxidase, allopurinol prevents the formation of uric acid, thus lowering its concentration in the body. This is an example of inhibiting a key enzyme in a metabolic pathway to achieve a therapeutic effect.

The correct option is A.
$\boxed{\text{A. Allopurinol}}$