Warfarin has been the mainstay of oral anticoagulant
therapy for the past 60 years and it is most
commonly used to treat or prevent thrombosis or
thromboembolism in patients with venous thromboembolism,
atrial fibrillation and prosthetic heart
valves.1 However, this drug is efficacious only when
the dosage is maintained within a narrow therapeutic
index, measured by the international normalized
ratio (INR). Multiple challenges exist in
appropriately achieving and maintaining therapy
within this narrow index. Recent data have identified
genetic variants that may reduce a person’s
requirement for warfarin.2,3 Furthermore, once a
suitable dosage of warfarin has been established,
control of therapy can be affected by changes in
intake of vitamin K, development of acute medical
conditions (e.g., fever, diarrhea), changes in certain
chronic medical conditions (e.g., heart failure) and
interactions with prescription, nonprescription
and herbal products.1