Drug Interaction Report

MONITOR: Administration of radiolabeled ibritumomab tiuxetan (after pretreatment with rituximab) results in severe and prolonged cytopenia that is generally reversible, and the risk may be increased after prior therapy with fludarabine-containing regimens. In a clinical trial in which yttrium-90 radiolabeled ibritumomab tiuxetan was administered as consolidation after prior first-line chemotherapy, a higher frequency of severe and prolonged neutropenia and thrombocytopenia was observed in patients who had received yttrium-90 radiolabeled ibritumomab tiuxetan within 4 months after a combination chemotherapy of fludarabine with mitoxantrone and/or cyclophosphamide compared to those who had received any other chemotherapy.

MANAGEMENT: Clinicians should be aware that there may be an increased risk of hematologic toxicity when radiolabeled ibritumomab tiuxetan is administered shortly (within 4 months) after fludarabine-containing regimens. Complete blood cell and platelet counts should be monitored closely in accordance with product labeling recommendations.