Tehran University of Medical Sciences Archives of Anesthesiology and Critical Care 2423-5849 0 0 2025 11 15 1361 1361 Hossein Karballaei Mirzahosseini Department of Clinical Pharmacy, School of Pharmacy Semnan University of Medical Science, Semnan, Iran. Leili Manafi Department of Clinical Pharmacy, Kosar Hospital, Semnan, Semnan University of Medical Sciences, Semnan, Iran. 2025 08 01 2025 08 10 In certain patients, particularly those receiving mechanical aortic valve replacement, warfarin is the sole permitted anticoagulant. Some individuals exhibit resistance to warfarin for a variety of reasons, necessitating extremely high and occasionally fatal doses of the medication for their survival. This report details a patient who demonstrates warfarin resistance and investigates the fundamental causes of this phenomenon. The case report emphasizes the possible role of genetic polymorphism in elucidating the mechanisms behind warfarin resistance. https://aacc.tums.ac.ir/index.php/aacc/article/view/1361