Introduction:

When assessing the need for a cardiac valvular surgical replacement, it is possible to choose between a mechanical or bioprosthetic valve; The choice must take into account the risks of anticoagulant therapy and the potential need and/or risk of new interventions. Anticoagulation is performed with vitamin K antagonists and warfarin is the most commonly prescribed of these. This medicine due to its hepatic metabolism (P450) has multiple pharmacological and non-pharmacological interactions that sometimes become a real problem in clinical practice. To date, it is not recommended to routinely perform a genotype-guided dosage. However, such genetic studies are necessary to define medical behaviors when handling is difficult.

Case report:

It is described a case of a 37-year-old woman with a mechanical mitral valve due to rheumatic disease, chronically anticoagulated with warfarin; however, during the follow-up with multiple emergency consultations (2-3 times per month) for anticoagulation levels in subtherapeutic ranges such as elevated INR levels. She presented acute myocardial infarction with healthy coronary arteries and transient cerebral ischemia in the context of low INR thus considered thromboembolic etiology. Due to these difficulties, it was decided to measure coagulation factor II levels, which was normal despite the use of the drug, suspecting drug resistance. A genetic study was requested that showed genotype associated with reduced or normal CYP2C9 enzymatic activity, plus a WARF CYP2C9 * 1/* 2 and WARF VKORC1 A/A genotype concluding that the patient presented a divergent metabolic behavior for warfarin. It was decided to perform a mechanical valve replacement with a bioprosthetic valve, in order to suspend the use of warfarin. The patient presented a satisfactory clinical evolution.

Conclusions:

Pharmacogenetics has managed to identify polymorphisms in the genes involved in warfarin metabolism, which are related to bleeding risk. These variants are related to the CYP2C9, CYP4F2 and VKORC1 genes. Although no clinical impact has been demonstrated in genotype-guided warfarin adjustments, such tests are necessary in some cases to suggest a change in the dose of the medication or the definitive suspension.

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