Warfarin Therapy: New Challenges of an Old Drug

The anticoagulant drug warfarin is a vitamin K antagonist (VKA), coumarin derivative, formed by the racemic mixture of two optically active isomers known by Rectus (R) and Sinister (S) enantiomers in equal proportion, being the S-warfarin five times more potent. Although warfarin is still considered the mainstay of oral anticoagulant treatment, it is a difficult drug to manage due to its narrow therapeutic index. An inappropriate management of patients can lead to subtherapeutic or supratherapeutic levels, increasing the risk of thromboembolic episodes or hemorrhagic episodes, respectively. Common indications for the use of warfarin include stroke prevention in atrial fibrillation, preventing thrombus formation in patients with heart valves and treatment of venous thromboembolism. Unlike situations as nonvalvular atrial fibrillation (and thromboembolic risk factors such as hypertension, diabetes or ventricular dysfunction), venous thrombosis and pulmonary embolism where there is evidence for the use of the new oral anticoagulants (dabigatran, apixaban, rivaroxaban, etc), warfarin and similar remain only option for patients with cardiac valve prosthesis requiring anticoagulation.