Warfarin resistance: possibilities to solve this problem. A case report.

Effective prevention of thromboembolism is essential for patients with mechanical prosthetic heart valves. For this group of patients, vitamin K antagonists (VKAs) remain the drug group of choice despite the widespread use of new anticoagulants in other diseases. As a consequence, warfarin resistance remains a serious challenge for physicians. The current report describes a 65-year-old male patient that had a mechanical prosthetic aortic valve implanted due to severe aortic insufficiency after infective endocarditis. Despite consistent increases in his warfarin dose, the level of international normalized ratio (INR) remained very low. The patient was considered to have warfarin resistance. Warfarin was successfully replaced by another VKA, acenocoumarol, which resulted in a stable INR observed over 1 year of follow-up. Achieving the target INR in patients with mechanical prosthetic heart valves using VKAs is the main goal of thromboprophylaxis. Although the genetic changes that cause warfarin resistance are understood, the options to overcome these pharmacogenetic issues remain limited. Based on the success with this current patient, physicians with similar patients with warfarin resistance might wish to consider replacing warfarin with acenocoumarol.