Question

A patient with Burkitt lymphoma develops tumor lysis syndrome with uric acid $>$ 12 mg/dL and serum creatinine 3.5 mg/dL. What is the most appropriate next management step?

• A. Allopurinol + hydration
• B. Rasburicase + hydration
• C. Fluid restriction
• D. Hemodialysis

Hint:

Hyperuricemia Management in Tumor Lysis Syndrome (TLS):
- Low/Intermediate Risk (Prophylaxis): Allopurinol + Hydration (prevents new uric acid formation).
- High Risk or Established TLS Renal Impairment Uric acid $>8\text{ mg/dL}$: Rasburicase + Hydration (actively degrades existing uric acid to water-soluble allantoin).
- Caution: Screen for G6PD deficiency before Rasburicase (risk of severe methemoglobinemia and hemolysis).

Answer 1

The Correct Option is B

Concept:
Burkitt lymphoma is a high-grade, rapidly proliferating non-Hodgkin lymphoma with an extremely high cell turnover rate, placing patients at the highest risk for developing fulminant Tumor Lysis Syndrome (TLS).
Severe hyperuricemia causes precipitation of uric acid crystals within the renal collecting ducts and distal tubules, leading to acute uric acid nephropathy and acute kidney injury (elevated creatinine).
Explanation:
• In established clinical Tumor Lysis Syndrome with existing severe hyperuricemia ($\text{uric acid} > 12\text{ mg/dL}$) and acute renal impairment ($\text{serum creatinine} = 3.5\text{ mg/dL}$), the immediate drug of choice is Rasburicase along with vigorous intravenous hyperhydration without potassium/phosphate.

• Rasburicase is a recombinant urate oxidase enzyme that rapidly catalyzes the enzymatic conversion of poorly soluble uric acid into allantoin, an inactive metabolite that is 5 to 10 times more water-soluble and excreted freely by the kidneys.

• Allopurinol acts only as a competitive inhibitor of the enzyme xanthine oxidase, preventing the de novo formation of new uric acid, but it does NOT break down or degrade existing uric acid pools already accumulated in the blood and renal tubules.

• Furthermore, allopurinol leads to accumulation of xanthine and hypoxanthine, which can themselves precipitate in the renal parenchyma (xanthine nephropathy).

• Fluid restriction is strictly contraindicated because aggressive intravenous hyperhydration ($2.5\text{--}3\text{ L/m}^2\text{/day}$) is required to maintain high renal tubular flow and flush crystalloids out of the kidneys.

• Renal replacement therapy (hemodialysis) is reserved for patients who remain refractory to medical management (severe intractable hyperkalemia, severe volume overload/anuria, or persistent hyperphosphatemia).
Final Answer:
The most appropriate immediate pharmacologic and supportive intervention for established severe hyperuricemia with renal impairment is recombinant urate oxidase (Rasburicase) along with aggressive intravenous hydration.