Administration of Immune Checkpoint Inhibitors to Patients on Warfarin May Elevate PT-INR

The relationship between the concomitant use of immune checkpoint inhibitors (ICIs) and elevated prothrombin time-to-international standard ratio (PT-INR) in patients receiving warfarin remains unclear. In the present study, 26 patients treated with ICIs during warfarin therapy were examined for increases in PT-INR within 60 d of ICI administration. Of these patients, 13 developed Grade 2 or higher PT-INR elevations, 5 of which required the immediate administration of vitamin K. The increased risk of bleeding and the impact on the continuation of cancer drug therapy are significant burdens for patients. Immune-related adverse events caused by ICIs have been suggested as one of the reasons for increases in PT-INR, and patients taking warfarin and ICIs need to be managed in consideration of the risk of elevated PT-INR by frequently checking the blood coagulation capacity.