A 42-year-old man is hospitalized to begin chemotherapy for recently diagnosed Burkitt-like lymphoma. He is started on aggressive intravenous volume repletion with isotonic sodium chloride and allopurinol. Three days into receiving hyper-CVAD therapy (cyclophosphamide, vincristine, doxorubicin, dexamethasone), he develops decreasing urine output to 0.6 mL/kg/h. His only other medication is as-needed ondansetron.
On physical examination, blood pressure is 130/72 mm Hg. There is lymphadenopathy involving the cervical and submental chains and supraclavicular areas bilaterally, as well as bulky axillary and inguinal lymphadenopathy. Heart rate and rhythm are regular. Lungs are clear. The spleen is palpable approximately 4 cm below the left costal margin. There is no hepatomegaly. There is no edema, cyanosis, or clubbing of the extremities.
Blood urea nitrogen | 22 mg/dL (7.9 mmol/L) |
Calcium | 7.3 mg/dL (1.8 mmol/L) (baseline, 8.7 mg/dL [2.2 mmol/L]) |
Creatinine | 1.3 mg/dL (114.9 µmol/L) (baseline, 0.9 mg/dL [79.6 µmol/L]) |
Phosphorus | 6.5 mg/dL (2.1 mmol/L) (baseline, 3.3 mg/dL [1.1 mmol/L]) |
Potassium | 5.1 mEq/L (5.1 mmol/L) (baseline, 4.3 mEq/L [4.3 mmol/L]) |
Urate | 14 mg/dL (0.83 mmol/L) (pretreatment level, 6.2 mg/dL [0.37 mmol/L]) |
Urinalysis | pH 5.5; multiple urate crystals |
Which of the following is the most appropriate treatment?