What can prevent tumor lysis syndrome in a male B cell lymphoma patient post-chemotherapy with hyperkalemia, hypocalcemia, hyperphosphatemia, and impaired renal function?

Allopurinol Prevents Tumor Lysis Syndrome in High-Risk B-Cell Lymphoma Patients

The correct answer is B. Allopurinol, which should be initiated at least 48 hours before chemotherapy to prevent tumor lysis syndrome (TLS) in patients with B-cell lymphoma at high risk for this life-threatening complication. 1

Why Allopurinol is the Preventive Agent

Allopurinol prevents the formation of uric acid by inhibiting xanthine oxidase, thereby reducing the risk of uric acid crystallization in renal tubules that leads to acute kidney injury, the hallmark of TLS. 1 This patient's presentation—hyperkalemia (K=6), hypocalcemia, hyperphosphatemia, and severe renal impairment (urea 570)—represents established clinical TLS that could have been prevented with prophylactic allopurinol. 1, 2

Prophylactic Dosing Strategy

• Allopurinol should be started 24-48 hours before initiating chemotherapy in all patients with B-cell lymphoma, particularly those with high tumor burden, elevated LDH, or bulky disease. 1, 3
• The standard prophylactic dose is 300 mg orally once daily in adults. 1
• For patients already at high risk (elevated baseline uric acid, high white blood cell count >50,000/mm³, or extensive bone marrow involvement), rasburicase may be preferred over allopurinol for prophylaxis. 4, 2

Why the Other Options Are Incorrect

Thiazide Diuretics (Option A) - Contraindicated

Thiazide diuretics are absolutely contraindicated in TLS prevention because they decrease uric acid excretion, potentially worsening hyperuricemia and precipitating uric acid nephropathy. 1 Thiazides would exacerbate rather than prevent this presentation.

Furosemide (Option C) - Adjunctive Only, Not Preventive

Loop diuretics like furosemide play only an adjunctive role in TLS management to maintain urine output once adequate hydration is established—they do not prevent TLS and should never be used as monotherapy. 1, 4

• Furosemide is indicated only when urine output falls below 100 mL/hour despite aggressive IV hydration. 1
• Loop diuretics are contraindicated in patients with hypovolemia or obstructive uropathy, and they do not address the underlying metabolic derangements of TLS. 1
• They cannot prevent the massive release of intracellular contents (potassium, phosphate, nucleic acids) that occurs with tumor cell lysis. 1

The Complete Prevention Strategy

Risk Stratification Before Chemotherapy

All patients with B-cell lymphoma should undergo risk assessment for TLS before initiating chemotherapy, with particular attention to tumor burden, baseline LDH, white blood cell count, and renal function. 2

• High-risk features include: bulky disease, elevated LDH, WBC >50,000/mm³, pre-existing renal impairment, elevated baseline uric acid, and extensive bone marrow involvement. 2, 3
• B-cell lymphomas, particularly Burkitt's lymphoma and diffuse large B-cell lymphoma, carry the highest TLS risk among lymphoid malignancies. 2, 5, 6

Prophylactic Regimen Components

The standard prevention protocol combines allopurinol with aggressive IV hydration starting 24-48 hours before chemotherapy. 1

1. Allopurinol 300 mg orally once daily, initiated 24-48 hours pre-chemotherapy 1
2. Aggressive IV hydration (typically 3 L/m²/day) to maintain urine output ≥100 mL/hour 1
3. Baseline laboratory monitoring: comprehensive metabolic panel, LDH, uric acid, phosphate, calcium, and potassium 1

When to Upgrade to Rasburicase

For patients at very high risk or those who develop laboratory TLS despite allopurinol prophylaxis, rasburicase should replace allopurinol as it rapidly degrades existing uric acid rather than merely preventing its formation. 1, 4

• Rasburicase is dosed at 0.2 mg/kg IV over 30 minutes. 7
• Never administer allopurinol concurrently with rasburicase, as this removes the substrate for rasburicase and causes xanthine accumulation. 4
• Rasburicase is contraindicated in patients with G6PD deficiency due to risk of severe hemolysis. 7

Critical Monitoring After Prevention Initiation

Once prophylaxis begins, monitor electrolytes, renal function, and uric acid every 12 hours for the first 3 days after chemotherapy initiation. 1

• Potassium, phosphate, calcium, uric acid, creatinine, and BUN should be checked every 12 hours initially. 1
• Urine output must be monitored hourly to ensure ≥100 mL/hour is maintained. 1
• Any patient developing laboratory TLS (≥2 metabolic abnormalities) despite prophylaxis requires immediate escalation to treatment-level interventions including rasburicase and consideration for dialysis. 1, 4, 2

Common Pitfalls to Avoid

The most critical error is failing to initiate prophylaxis before chemotherapy in high-risk patients—once TLS develops, mortality approaches 30% even with aggressive treatment. 3, 5, 6

• Do not wait for symptoms to appear before starting prophylaxis; TLS prevention must be proactive. 3
• Do not use urine alkalinization with rasburicase, as this increases calcium-phosphate precipitation. 1
• Do not treat asymptomatic hypocalcemia, as calcium administration worsens renal calcium-phosphate deposition. 1, 2
• Spontaneous TLS can occur even before chemotherapy in patients with high tumor burden, so prophylaxis should begin at diagnosis in very high-risk cases. 5, 6