title: A case report of a patient carrying CYP2C9*3/4 genotype with extremely low warfarin dose requirement.
abstract: We report a case of intolerance to warfarin dosing due to impaired drug metabolism in a patient with CYP2C9*3/*4. A 73-yr-old woman with atrial fibrilation was taking warfarin. She attained a high prothrombin time international normalized ratio (INR) at the standard doses during the induction of anticoagulation and extremely low dose of warfarin (6.5 mg/week) was finally chosen to reach the target INR. Genotyping for CYP2C9 revealed that this patient had a genotype CYP2C9*3/*4. This is the first Korean compound heterozygote for CYP2C9*3 and *4. This case suggests the clinical usefulness of pharmacogenetic testing for individualized dosage adjustments of warfarin.
authors.affiliation: Department of Laboratory Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Soo Youn
authors.initials: SY
authors.lastname: Lee
authors.forename: Myung Hyun
authors.initials: MH
authors.lastname: Nam
authors.forename: June Soo
authors.initials: JS
authors.lastname: Kim
authors.forename: Jong Won
authors.initials: JW
authors.lastname: Kim
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D001281:Atrial Fibrillation / Q000188:drug therapy* / Q000235:genetics*; D065729:Cytochrome P-450 CYP2C9; D005260:Female; D005838:Genotype; D006579:Heterozygote; D006801:Humans; D019934:International Normalized Ratio; D010597:Pharmacogenetics; D011110:Polymorphism, Genetic; D011517:Prothrombin Time; D014859:Warfarin / Q000494:pharmacology*
chemical_list: D000925:Anticoagulants; D014859:Warfarin; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases