Oral anticoagulants are effective for primary and secondary prevention of venous thromboembolism; for prevention of systemic embolism in patients with prosthetic heart valves or atrial fibrillation; for prevention of acute myocardial infarction (AMI) in patients with peripheral arterial disease and patients otherwise at high risk, for prevention of stroke, recurrent infarction and to reduce mortality in patients with AMI.
Physicians are reluctant to prescribe warfarin, in part because they fear that the drug will cause bleeding. Patients treated with warfarin do require close monitoring to avoid bleeding. It has been shown that the drug significantly reduces stroke rates and for these indications, a moderate anticoagulant intensity (range, INR 2.0-3.0) is recommended.5
- Some countries use warfarin, while others use different VKAs, such as acenocoumarol or phenprocoumon. These VKAs have a shorter (acenocoumarol) or longer (phenprocoumon) half-life, and are not completely interchangeable with warfarin.
- Generic VKAs are sold in some countries; these are also not totally interchangeable to warfarin
- VKAs can be administered orally. They have a narrow therapeutic window, have a slow onset of action and may have unpredictable pharmacology. In addition, many foods and drugs interact with VKAs. As a result, periodic blood tests and dose adjustments are necessary to maintain the optimal degree of anticoagulation.1