Allopurinol functions in TLS prevention by inhibiting xanthine oxidase to reduce uric acid production. Which statement is true?

• A. It reduces uric acid production but does not rapidly lower existing uric acid levels.
• B. It rapidly lowers existing uric acid levels.
• C. It increases uric acid production.
• D. It has no role in TLS.

Answer: (A)

Allopurinol works by blocking xanthine oxidase, so it stops the formation of new uric acid. That means it lowers the amount of uric acid being produced, which is helpful for preventing tumor lysis syndrome. But it doesn’t act on uric acid that’s already in the blood or tissues, so it doesn’t rapidly reduce those existing levels. For a quick drop in uric acid during TLS, another agent like rasburicase is used because it directly degrades already formed uric acid. So the statement that best fits is that it reduces uric acid production but does not rapidly lower existing uric acid levels.