ABSTRACT

Warfarin resistance is a rare but an important clinical problem in patients requiring anticoagulation. Here we report a male patient with a mechanical aortic prosthetic valve who did not have a target level of therapeutic anticoagulation on warfarin. A pharmaco-genetic testing revealed VKORC1 A/G and CYP2C9 *1*1 genotype. His prothrombin time level with international normalization ratio (INR) was 1–1.3 on warfarin 80 mg per day. Phenprocoumon was not successful to increase INR level. He has been given enoxaparine BID (1 mg/kg) without any thromboembolic events at follow-up. Although VKORC1 and CYP2C9 genes are two major genetic factors responsible for this clinical situation, more studies seem to be necessary to explain this phenomenon.