Single 6-mg dose of rasburicase: The experience in a large academic medical center.

BACKGROUND: Tumor lysis syndrome is an oncologic emergency due to the release of tumor cell contents, leading to metabolic derangements. Rasburicase, a recombinant urate oxidase, catabolizes uric acid. At our institution, we administer a single 6-mg dose of rasburicase to patients who are at risk for tumor lysis syndrome. We aimed to assess the efficacy of single 6-mg dose of rasburicase and explore risk factors associated with rasburicase failure.

METHODS: We report results in 92 adult patients who had a baseline uric acid greater than 7.5 mg/dL and received a single 6-mg dose of rasburicase for the management of tumor lysis syndrome. Responders were defined as those whose uric acid was less than or equal to 7.5 mg/dL within 24-36 h of rasburicase administration. The primary end point was response based on uric acid level. Secondary end points included response to rasburicase in association with lactate dehydrogenase, serum creatinine, calcium, phosphorus, blood pH, and oncologic diagnosis.

RESULTS: Median age was 65 years and 70% were men. Most patients had leukemia (32%) or lymphoma (40%). Eighty-seven of 92 patients (95%), who received single 6-mg dose of rasburicase, achieved a uric acid less than 7.5 mg/dL within 24-36h of dosing. Body mass index was similar between responders and non-responders: 28.6 kg/m2 vs. 26.6 kg/m2 , respectively, p = 0.6. Baseline lactate dehydrogenase levels were similar between the groups: 756 U/L vs. 892 U/L, respectively, p = 0.33. Blood pH values documented within 24 h of first dose of rasburicase were also similar between the two groups (n = 30; 7.33 vs. 7.34 respectively, p = 0.6). However, median baseline uric acid was lower in responders than non-responders: 12.3 mg/dL vs. 17.3 mg/dL, respectively, p = 0.012. Baseline serum creatinine and creatinine clearance were similar between responders and non-responders (2.2 mg/dL vs. 3.95 mg/dL; p = 0.12 and 29 mL/min vs. 16 mL/min; p = 0.11, respectively).

CONCLUSIONS: Higher baseline uric acid levels were observed in patients who did not respond to the first rasburicase dose. In our study, uric acid levels normalized in 95% of patients after a single 6-mg dose of rasburicase indicating that a single 6-mg dose of rasburicase may be sufficient to manage tumor lysis syndrome, for most patients.