Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 3 3 2019 01 15 90 93 Masuod Malekzadeh Digestive Disease Research Center Digestive Disease Research Institute, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Marzieh Pazoki Department of Pulmonary and Critical Care Medicine, Sina Medical Center, Tehran University of Medical Sciences, Tehran, Iran. 2018 08 28 2018 11 10 Warfarin resisance was known as subtherapeutic INR (International Normalized Ratio) in spite of normally prescribed doses of warfarin. There are few reports of warfarin resisance from Iran. In this article, we report a 43-year-old man with a hisory of deep vein thrombosis who took 10 mg of warfarin and 120 mg of enoxaparin daily. He was presented with new acute deep vein thrombosis while taking anticoagulants. Despite warfarin dose increase to 50 mg, the INR did not achieve the therapeutic level. His genetic tesing was negative for VKORC1 mutation but positive for CYP2C9*3, which proposed other underlying mechanisms for his warfarin resisance. This report added to the cases of warfarin resisance in Iran and herald more attention to warfarin metabolism and its interaction. Also it calls for checking serum warfarin level and Factor II and Factor X level for better evaluating compliance in patients presented with warfarin resistance. https://crcp.tums.ac.ir/index.php/crcp/article/view/214 https://crcp.tums.ac.ir/index.php/crcp/article/download/214/275