Warfarin is one of the most widely used drugs in the world for a variety of indications involving the prevention and treatment of thromboembolic phenomena. Even after 60 years of its use, warfarin's narrow threshold of toxicity, combined with its dose-response ratio and the many factors that determine how well it works in humans, supports its continued evaluation by researchers around the world.
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One primary consideration in the use of warfarin is whether there are any contraindications to its use. These may be absolute, forbidding its use under any circumstances whatsoever, or relative, in which case the physician needs to balance the risks of bleeding complications against the risks of thromboembolism posed by the disease condition requiring warfarin therapy.
Absolute contraindications
Some of the absolute contraindications to warfarin include:
- Large esophageal varices
- Patients who have undergone major surgery within the last 72 hours
- A platelet count less than 50 x 109/cu.mm, which constitutes significant thrombocytopenia
- Hypersensitivity to the drug, such as skin ischemic necrosis or priapism
- A clinically significant bleeding condition; however, the patient's risks of warfarin can be reassessed after three months
- Pregnancy and within 48 hours of delivery because of warfarin's known teratogenicity, as well as its capacity to induce spontaneous abortion and fetal/perinatal bleeding
- Coagulation defects at baseline such that the international normalized ratio (INR) is over 1.5
- Decompensated liver disease
Relative contraindications
Relative contraindications require a careful balancing of the risks of warfarin against the risks of thromboembolism before making a decision to administer the drug. These relative contraindications include:
- Previous history of intracranial hemorrhage
- Recent history of a major extracranial bleed without known cause
- History of peptic ulceration within the past three months. In these cases, it is recommended that the patient waits to begin warfarin therapy until treatment of peptic ulcer is completed.
- Recent history of repeated falling episodes with a patient at a higher risk for bleeds
- Likelihood of poor patient compliance due to dementia or cognitive impairment, particularly in cases when there is no available caretaker.
- Alcoholism, especially binge drinking
- Poorly controlled or untreated hypertension
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