title: Major bleeding caused by warfarin in a genetically susceptible patient.
abstract: A 90-year-old woman was hospitalized for gastrointestinal bleeding. Although she had been receiving only warfarin 5 mg/day, her international normalized ratio (INR) was 66. Warfarin was discontinued, and her INR fell to 3.7 after transfusion of fresh-frozen plasma. However, it rose again spontaneously to 7.5. Eleven days after the last dose of warfarin had been administered, it was still detectable in the patient's plasma, indicating that impaired warfarin clearance may have caused an enhanced anticoagulation effect. Genetic analysis of the cytochrome P450 (CYP) isoenzyme 2C9, which mediates the major deactivating pathway of S-warfarin, revealed that the patient was a compound heterozygote carrying two variant alleles: CYP2C9*2 and CYP2C9*3. The patient's enhanced sensitivity to warfarin 5 mg/day can be ascribed to decreased clearance of S-warfarin secondary to genetic alteration of the gene encoding CYP2C9, resulting in a life-threatening complication.
authors.affiliation: Division of Medicine, Hadassah University Hospital, Jerusalem, Israel.
authors.forename: Aharon
authors.initials: A
authors.lastname: Bloch
authors.forename: Eldad
authors.initials: E
authors.lastname: Ben-Chetrit
authors.forename: Mordechai
authors.initials: M
authors.lastname: Muszkat
authors.forename: Yoseph
authors.initials: Y
authors.lastname: Caraco
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000009:adverse effects* / Q000097:blood / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006471:Gastrointestinal Hemorrhage / Q000139:chemically induced* / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D006207:Half-Life; D006801:Humans; D019934:International Normalized Ratio; D011110:Polymorphism, Genetic; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism; D014859:Warfarin / Q000009:adverse effects* / Q000097:blood / Q000378:metabolism
chemical_list: D000925:Anticoagulants; D014859:Warfarin; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase