Single 4.5 mg fixed-dose of rasburicase for hyperuricemia associated with tumor lysis syndrome.

Rasburicase is a recombinant urate oxidase enzyme administered for treatment of hyperuricemia associated with tumor lysis syndrome. Studies demonstrate effectiveness of single fixed-dose rasburicase as compared to the FDA-approved dose of 0.2 mg/kg intravenously daily for up to five days. Doses in these studies range from 1.5 mg to 7.5 mg. Our study evaluated outcomes in patients who received single 4.5 mg fixed-dose rasburicase. This retrospective, IRB-approved chart review evaluated adult oncology subjects who received fixed-dose rasburicase between January 2007 and April 2014. The primary outcome was percentage of patients with normalization of uric acid (level <8 mg/dL within 24 h) after a single 4.5 mg fixed-dose of rasburicase. Secondary objectives were incidence of initial failure of fixed-dose rasburicase and normalization of uric acid in overweight (body mass index ≥25 kg/m2) versus non-overweight patients. Initial failure was defined as need for additional doses or progression to dialysis within one week of the initial fixed-dose. In the 128 patients included, the mean baseline uric acid level was 14.84 mg/dL. Of the 112 patients with a follow-up uric acid level, 68% achieved normalization within 24 h of rasburicase administration. Thirty-eight patients received additional treatment: 10 received additional dose(s) and 28 underwent dialysis. Normalization of uric acid in overweight versus non-overweight patients was 66% and 73%, respectively. Overall, a single 4.5 mg fixed-dose of rasburicase effectively normalized uric acid in 68% of patients within 24 h. Further studies are needed to determine the optimal single fixed-dose necessary for treatment response across all patients.