Probable interaction between warfarin and antitumor agents used in R-ESHAP chemotherapy

Background: The pharmacologic effects of warfarin might be altered by various factors, including drug-drug interaction.Case summary: A 49-year-oold Japanese man (height, 174 cm; weight, 68 kg) presented with a 20-month history of malignant lymphoma (diffuse large B cell lymphoma, clinical stage IV). He was treated with a combination of rituximab chemotherapy and etoposide, cisplatin, high-dose cytarabine, and methyl-prednisolone (R-ESHAP). He had been receiving warfarin for the secondary prevention of pulmonary embolism with deep venous thrombosis. When R-ESHAP was started, international normalized ratio (INR) increased from 1 to 5. This phenomenon was observed again in the second R-ESHAP. The INR was increased from 2.44 to 4.71 during chemotherapy but was returned to within the normal range (1.05; normal range: 0.81-1.009) 5 days after chemotherapy was completed.Conclusion: In this patient, R-ESHAP chemotherapy might have affected warfarin anticoagulation sensitivity; thus, careful monitoring of INR is essential, particularly in patients receiving warfarin who underg go R-ESHAP chemotherapy.