What is the mechanism by which allopurinol helps prevent uric acid buildup in tumor lysis syndrome?

• A. It reduces uric acid production
• B. It directly converts uric acid to allantoin
• C. It increases phosphate excretion
• D. It cures TLS

Answer: (A)

Allopurinol works by inhibiting xanthine oxidase, the enzyme that converts hypoxanthine and xanthine into uric acid during purine breakdown. In tumor lysis syndrome, a rapid surge of nucleic acids from dying tumor cells increases purine catabolism, raising uric acid levels and risking uric acid–related kidney injury. By blocking xanthine oxidase, allopurinol lowers the amount of uric acid produced, helping prevent its buildup. It does not directly convert uric acid to allantoin (that role belongs to uricase enzymes like rasburicase, which humans lack), and it does not by itself cure TLS or alter phosphate excretion.