Which statement about TLS prophylaxis is correct?

• A. Allopurinol prevents uric acid formation; rasburicase rapidly metabolizes existing uric acid
• B. Rasburicase prevents uric acid formation; allopurinol metabolizes existing uric acid
• C. Both do the same
• D. Neither helps

Answer: (A)

TLS prophylaxis targets uric acid to prevent kidney injury from tumor lysis. Allopurinol blocks xanthine oxidase, which reduces the formation of uric acid from purines, so less uric acid is produced. It does not remove uric acid that’s already in the body. Rasburicase, by contrast, is an enzyme that converts existing uric acid into allantoin, a more soluble compound, leading to a rapid drop in uric acid levels. Because of these different actions, the statement that allopurinol prevents uric acid formation and rasburicase rapidly metabolizes existing uric acid reflects their distinct roles most accurately. Rasburicase does not prevent formation, and allopurinol does not metabolize existing uric acid, so the other descriptions don’t fit.