Supratherapeutic INR resulting from the initiation of warfarin in a patient receiving axitinib.

Axitinib is a vascular endothelial growth factor receptor inhibitor indicated for advanced renal cell cancer after failure of one prior systemic therapy. We report a case where a patient receiving axitinib experienced a supratherapeutic INR soon after initiation of an age-appropriate warfarin dose. We propose two possible mechanisms for this interaction, including competitive protein binding and decreased metabolism. Close INR monitoring and dose adjustments of warfarin may be necessary in patients receiving concomitant axitinib and warfarin in order to decrease the risks associated with this interaction.