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Zorluk: Çok zorHematology and Oncology

A 22-year-old man is admitted to the hospital for initiation of induction chemotherapy for recently diagnosed Burkitt lymphoma. His medical history is significant for an episode of acute jaundice, fatigue, and dark urine two years ago after taking primaquine for malaria prophylaxis; the episode spontaneously resolved upon discontinuation of the medication. The patient currently feels well and reports no symptoms. His temperature is 37.1°C (98.8°F), blood pressure is 120/78 mm Hg, and pulse is 82/min. Physical examination reveals prominent cervical and axillary lymphadenopathy but is otherwise unremarkable.

Laboratory studies show:
LabValueReference Range
Hemoglobin13.8 g/dL13.5-17.5 g/dL
Leukocyte count18,500/mm³4,500-11,000/mm³
Platelet count210,000/mm³150,000-400,000/mm³
Blood urea nitrogen18 mg/dL8-20 mg/dL
Serum creatinine1.2 mg/dL0.7-1.3 mg/dL
Potassium4.6 mEq/L3.5-5.0 mEq/L
Calcium8.8 mg/dL8.4-10.2 mg/dL
Phosphorus4.9 mg/dL2.5-4.5 mg/dL
Uric acid14.2 mg/dL4.0-8.0 mg/dL
Lactate dehydrogenase1,850 U/L100-250 U/L

The patient is started on aggressive intravenous normal saline hydration. Which of the following is the most appropriate next step in the management of this patient's hyperuricemia?

  1. Administration of intravenous allopurinolCevap
  2. B
    Administration of intravenous rasburicase
  3. C
    Administration of intravenous sodium bicarbonate
  4. D
    Administration of oral probenecid
  5. E
    Initiation of urgent hemodialysis

Cevap

The most appropriate next step is the administration of intravenous allopurinol because rasburicase is contraindicated in patients with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency.
The correct answer is the administration of intravenous allopurinol. This patient has newly diagnosed Burkitt lymphoma (a highly proliferative tumor) and an elevated uric acid level of 14.2 mg/dL, placing him at high risk for Tumor Lysis Syndrome (TLS). While rasburicase (a recombinant urate oxidase) is the preferred treatment for high-risk TLS with established hyperuricemia because it rapidly degrades existing uric acid into highly soluble allantoin, it is strictly contraindicated in this patient. His history of acute hemolysis following primaquine administration is pathognomonic for Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency. Rasburicase catalyzes the oxidation of uric acid, producing hydrogen peroxide (H2O2H_2O_2) as a byproduct. In G6PD deficiency, the inability to generate sufficient NADPH prevents the reduction of glutathione, neutralizing the oxidative stress from H2O2H_2O_2. This leads to severe, potentially fatal hemolysis and methemoglobinemia. Therefore, allopurinol, a xanthine oxidase inhibitor that prevents new uric acid formation without generating oxidative stress, is the most appropriate alternative.

Adım Adım Çözüm

1
Assess the patient's risk for Tumor Lysis Syndrome (TLS).
High risk due to newly diagnosed Burkitt lymphoma and a significantly elevated uric acid level of 14.2 mg/dL.
Identifying the severity of TLS risk determines the aggressiveness of the urate-lowering therapy required.
2
Determine the standard of care for high-risk TLS with established hyperuricemia.
Rasburicase (recombinant urate oxidase) is typically the first-line pharmacologic intervention.
Rasburicase rapidly degrades existing uric acid, whereas allopurinol only prevents the formation of new uric acid.
3
Evaluate the patient's medical history for contraindications.
The history of primaquine-induced hemolysis indicates Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency.
Primaquine is a classic oxidative trigger that causes acute hemolytic anemia in G6PD deficient individuals.
4
Select the safest alternative urate-lowering therapy.
Intravenous allopurinol must be administered instead of rasburicase.
Rasburicase generates hydrogen peroxide (H2O2H_2O_2) and is strictly contraindicated in G6PD deficiency; allopurinol is the appropriate alternative.

Anahtar Kavram

Rasburicase is contraindicated in patients with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency due to the risk of severe hemolysis and methemoglobinemia from hydrogen peroxide accumulation.
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Hematology and Oncology

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