**Question:** Which of the following describes the action of allopurinol

A. Inhibits xanthine oxidase
B. Increases uric acid clearance
C. Increases uric acid production
D. Increases uric acid excretion

**Core Concept:** Allopurinol is a drug used to treat hyperuricemia and gout. It primarily works by inhibiting xanthine oxidase, which is the rate-limiting enzyme in the purine catabolism pathway and is responsible for converting hypoxanthine to xanthine and then to uric acid.

**Why the Correct Answer is Right:** Allopurinol inhibits xanthine oxidase, leading to a decrease in the production of uric acid. As a result, the levels of uric acid in the body are reduced, helping to manage hyperuricemia and gout symptoms.

**Why Each Wrong Option is Incorrect:**

B. Increasing uric acid clearance or excretion is not the primary action of allopurinol. In fact, it would counteract the drug's intended effect, making this option incorrect.

C. Increasing uric acid production goes against the primary action of allopurinol in reducing uric acid levels. This option is incorrect.

D. Allopurinol increases uric acid excretion, which is the opposite of its primary action. This option is incorrect.

**Clinical Pearl:** Understanding the correct action of allopurinol is essential for correctly prescribing and interpreting its effects in clinical practice. Knowing the drug's mechanism helps to manage patients with hyperuricemia and gout effectively.

**Correct Answer:** A. Inhibits xanthine oxidase