Potential drug-drug interaction between tolvaptan and warfarin in a geriatric patient with heart failure.

Tolvaptan is a key drug for patients with heart failure. Here, we present a 92-year-old woman, whose PT-INR/dose increased from 1.74 to 3.30 after warfarin and tolvaptan co-administration, and resulted in a large cerebral infarction after warfarin dose down. Therefore, the interaction between these two drugs may be clinically significant.