Persistent drug interaction between aprepitant and warfarin in patients receiving anticancer chemotherapy

Case We describe two cases in which treatment with aprepitant persistently altered antithrombotic control in patients receiving warfarin. A 60-year-old man received 5 weekly cycles of chemotherapy. Aprepitant was administered as a 3-day regimen from the second cycle of chemotherapy. In each of the chemotherapy cycles that included aprepitant, the therapeutic international normalized ratio (INR) decreased markedly to <1.6, and slowly recovered over several weeks. A 47-year-old woman was treated with 4 weekly cycles of chemotherapy. Aprepitant was administered as a 3-day regimen. On day 8 of the first cycle of chemotherapy, the patient’s INR fell markedly to 1.1. Although warfarin dosage was steadily increased over the four subsequent cycles of chemotherapy, therapeutic target range was not recovered. INR gradually returned to normal during the 2 months after the final cycle of chemotherapy. Conclusion To our knowledge, this is the first case report to document the effects of aprepitant in cancer patients receiving anticoagulation therapy.