Drug Interactions between famotidine / ibuprofen and iodine i 131 tositumomab

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.

H2 antagonists may alter the pharmacokinetic disposition of some nonsteroidal anti-inflammatory drugs (NSAIDs), resulting in increased or decreased plasma concentrations. Data have been varied, even for the same NSAID. The mechanism may involve inhibition of metabolism, changes in gastric pH resulting in altered absorption, and/or reduced urinary elimination of the affected NSAIDs. Statistically significant changes have been small and of limited clinical significance when interactions have been observed.