Warfarin hypersensitivity in the internist's practice: a case report

Anticoagulants are widely used in clinical practice to reduce the risk of cardiovascular events. However, there are associated clinical conditions that require coagulation system monitoring due to an increased risk of bleeding. In clinical practice, cases of warfarin hypersensitivity due to gene polymorphisms are known. Taking warfarin in such a situation is often manifested by massive bleeding that threatens the patient's life. Sixty seven-years-old female patient was admitted to the internal medicine department of Rostov State Medical University clinic in March 2022. The day before, she noted severe abdominal pain, loose bloody stool. An outpatient examination revealed an increase in international normalized ratio to 9,42, thrombin time >30 sec. There were no signs of primary gastrointestinal pathology. According to anamnesis, on January 21, 2022, the patient underwent mechanical aortic valve replacement, in connection with which warfarin was prescribed at a dose of 2,5 mg/day. After establishing hypocoagulation, warfarin was discontinued. A pharmacogenetic analysis was performed, which established the carriage of polymorphisms of cytochrome P450 system genes, the homozygous mutation 1075A>C (CYP2C9 (*3/*3)), and the heterozygous mutation of the vitamin K reductase gene VKORC1 G(-1639)A (VKORC1 GA). The individual dosage of warfarin was calculated according to International Warfarin Pharmacogenetics Consortium guidelines, which was 9 mg/week. After adjusting the dose of warfarin, the level of international normalized ratio decreased to 3,61, thrombin time to 13 sec. The patient was discharged with recommendations to follow an individual warfarin regimen and monitor coagulation parameters. The presence of hypersensitivity to warfarin is not a reason for its complete withdrawal in situations requiring longterm anticoagulation. In this regard, it is necessary for the doctor to be vigilant when prescribing warfarin to a patient, understanding the causes and methods for diagnosing hypersensitivity to warfarin, and timely correction of its dosage.