2021 Volume 47 Issue 6 Pages 301-306
Warfarin (WF) has been reported to interact with various other drugs, but there are no reports of nivolumab or ipilimumab directly interacting with WF. In the current case, a patient taking WF had a prolonged PT and increased INR after combination therapy with nivolumab and ipilimumab. The patient was a 71-year-old man who was started on combination therapy with nivolumab and ipilimumab 2 months after excision of a renal tumor. PT-INR was 2.04 before admission. After combination therapy started, PT-INR increased to 8.58 according to a blood test performed on Day 22. The patient also developed hyperthyroidism, which is an immune-related adverse event (irAE) caused by nivolumab and ipilimumab. PT-INR increases as a result of hyperthyroidism, so the increase in PT-INR in the current patient is presumably due to irAE-induced hyperthyroidism. Thyroid dysfunction due to irAE may cause both hyperthyroidism and hypothyroidism and it may affect the efficacy of WF. PT-INR should be monitored when WF is used in combination with immune checkpoint inhibitors.
