In situations in which the risk of embolization is chronic, such as mechanical valves, atrial fibrillation, dilated cardiomyopathy with heart failure, and recurrent deep venous thrombosis, anticoagulation should be lifelong unless contraindications exist.
Duration after acute events (pulmonary embolism, deep venous thrombosis, acute anterior myocardial infarction) is controversial, but most clinicians maintain therapy for 4-6 months. Prophylactic use usually covers just the period of risk.
What factors increase the risk of bleeding during warfarin therapy?
a. Intensity of dose: INR values 3.0 have increased risk.
b. Age: Risk rises with increased age, but some find age not to be an independent risk factor.
c. Duration of therapy: The risk of bleeding is highest in the first several weeks of therapy: 3% risk in the first month, 0.8% risk per month in the first year, and 0.3% risk monthly for subsequent years. Cumulative risk increases with the duration of therapy.
d. Comorbid conditions: Cerebrovascular, renal, heart, and liver disease are associated with more bleeding complications.
e. Concurrent medications: Some drugs can predictably alter the PT/INR, but variability is the norm. When adding any new chronic medication, increase monitoring of PT/INR until a stable state is achieved.
f. Compliance: Safe, effective, outpatient warfarin use demands regular monitoring and systematic dose adjustments. Patient compliance is critical.