TLS prophylaxis in intermediate risk with G6PD deficiency

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A 50-year-old man with CKD G3b/A1, hypertension, and glucose-6-phosphate dehydrogenase (G6PD) deficiency is admitted to the hospital for a new diagnosis of acute myeloid leukemia. He is scheduled for induction chemotherapy with cytarabine and daunorubicin. Admission laboratory data: WBC count 50,000/µL (reference 4000–11,000); potassium 4.5 mEq/L (3.5–5.0); total CO₂ 24 mEq/L (23–28); creatinine 1.9 mg/dL (0.7–1.3); calcium 8.8 mg/dL (8.6–10.2); phosphorus 3.5 mg/dL (3.0–4.5). He is at intermediate risk for tumor lysis syndrome. In addition to volume expansion, which ONE of the following is the MOST appropriate treatment for preventing tumor lysis syndrome?

  1. A.Rasburicase
  2. B.AllopurinolCorrect
  3. C.Furosemide
  4. D.Sodium bicarbonate

Explanation

This patient at intermediate risk for tumor lysis syndrome (TLS) should receive allopurinol prophylaxis. TLS is an oncologic emergency characterized by the release of potassium, phosphate, and nucleic acids from massive tumor cell lysis. The risk of TLS depends on tumor type but is also influenced by other factors such as CKD. In general, solid tumors have a low risk for TLS, but there are exceptions, such as chemosensitive bulky tumors. Acute leukemias with WBC count 25,000–100,000/µL are intermediate risk. Highly aggressive lymphomas such as Burkitt and acute leukemias with WBC count >100,000/µL are high risk. CKD magnifies the baseline risk. Patients with intermediate risk, such as this one, should receive prophylaxis with allopurinol and IV volume expansion (usually referred to as “hydration”). Low-risk patients are managed with hydration alone. High-risk patients without contraindications should receive rasburicase (discussed below) in addition to hydration. All patients should be monitored for the development of TLS. The standard recommended dosing schedule for allopurinol is 300 mg/m²/day, up to a maximum of 800 mg daily. A dose reduction up to 50% can be considered in patients with decreased kidney function. Allopurinol 100 mg thrice daily is the most appropriate dose for preventing TLS in this patient and is much higher than the typical initial daily dose for gout prevention. Febuxostat is an alternative urate-lowering agent that has shown efficacy in the prevention and treatment of TLS and is an alternative for patients intolerant of allopurinol. Uric acid is more soluble at alkaline pH. However, urinary alkalinization is not recommended for TLS prophylaxis because it may increase the risk for calcium phosphate precipitation. Sodium bicarbonate IV would be a reasonable option for volume expansion in the presence of a non-anion gap metabolic acidosis. Routine use of diuretics for TLS prevention is not recommended unless clinical signs of volume overload are present. Rasburicase, a recombinant urate oxidase, is highly efficacious for both TLS prophylaxis and treatment. This agent is an appropriate choice for patients at high risk for TLS. Rasburicase is contraindicated in patients with G6PD deficiency because it may precipitate hemolytic anemia.

Why each option

A.
Rasburicase is reserved for high-risk TLS and is contraindicated in G6PD deficiency because hydrogen peroxide generation causes hemolysis and methemoglobinemia.
B.
Correct. AML with WBC 50,000/µL is intermediate TLS risk, managed with IV volume expansion plus allopurinol, renally adjusted for CKD.
C.
Loop diuretics are not used for TLS prevention unless volume overload develops; they do not lower uric acid production.
D.
Urinary alkalinization is no longer recommended because it promotes calcium phosphate precipitation in tubules without clear benefit for uric acid.

Reference: Cairo MS, Br J Haematol 2010 (recommendations for TLS risk classification and prophylaxis); Howard SC, N Engl J Med 2011 (the tumor lysis syndrome)

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