Background: Knowledge of the net benefit of warfarin therapy in routine care is needed to define realistic management recommendations, but lack of randomized controls precludes conventional risk-benefit analysis.
Objective: Assess risk and benefit of routine warfarin therapy in an anticoagulation clinic.
Design: Retrospective observational analysis.
Patients: A total of 1435 outpatients on warfarin for a total of 1613 patient years, treated to prevent the target events recurrent venous thromboembolism (VTE) or myocardial infarction (MI), and stroke in patients with atrial fibrillation (AF) or mechanical heart valves.
Measurements: Major bleeding and thromboembolic (TE) events and all deaths.
Calculations: Expected annual target event rates without warfarin were from published data. Differences between combined major events observed with warfarin, and expected without warfarin were calculated.
Results: In the total material, annual rates were 3.0% major TE events, 1.1% major bleeding events, 0.12% fatal bleeding, and a benefit/risk ratio of 3.8. The net gain, expressed in reduced combined bleeding and target TE annual event rate, was 9.9% in secondary prophylaxis in AF, 4.4% in VTE patients, 2.7% in post-MI patients, 2.4% in primary prophylaxis in AF and 0.6 in patients with mechanical heart valves. The apparent benefit/risk ratio was 3.9 in VTE patients, 5.8 in AF patients and 1.1 in patients with mechanical heart valves.
Conclusion: Net effects of prolonged warfarin therapy in patients with VTE and AF performed in an anticoagulation clinic have an acceptable risk/benefit ratio, comparable with what has been obtained in elective clinical trials.