Drug Interaction Report

MONITOR CLOSELY: Coadministration of tositumomab and iodine I 131 tositumomab with drugs that interfere with platelet function or coagulation may potentiate the risk of bleeding complications. Tositumomab and iodine I 131 tositumomab alone can cause severe or life-threatening thrombocytopenia. In premarketing clinical studies, NCI CTC grade 3 and 4 thrombocytopenia occurred in 53% of 230 patients, and sequelae included hemorrhage in 12% and requirement of platelet transfusions in 15% of patients. The time to thrombocyte nadir was 4 to 7 weeks and the duration of thrombocytopenia was approximately 30 days. However, 7% of the patients experienced thrombocytopenia that extended beyond 90 days following administration of the therapeutic regimen.

MANAGEMENT: Due to the frequent occurrence of severe and prolonged thrombocytopenia associated with tositumomab and iodine I 131 tositumomab, concomitant use of other medications that interfere with platelet function or coagulation should be considered cautiously. Close clinical and laboratory observation for bleeding complications is recommended during and after the therapeutic regimen. A complete blood count (CBC) with differential and platelet count should be obtained prior to and at least weekly for a minimum of 10 weeks after treatment.