A 10 mg warfarin initiation nomogram is safe and effective in outpatients starting oral anticoagulant therapy for venous thromboembolism

Abstract

The optimal means of initiating warfarin therapy for acute venous thromboembolism in the outpatient setting remains controversial. We have previously demonstrated the efficacy of a 10 mg initiation nomogram in a randomized controlled trial; however, some clinicians remain reluctant to use this nomogram due to a fear of potential increased bleeding. To review the safety and efficacy of a 10 mg warfarin nomogram we conducted a retrospective cohort study of patients prospectively treated for venous thromboembolism according to a 10 mg nomogram in an outpatient thrombosis clinic. All patients received standard treatment with low molecular weight heparin for 5 to 7 days and warfarin for at least 3 months. Four-hundred and fourteen patients were included in the analysis, of whom 295 (71%) fully adhered to the nomogram. In the whole cohort, 8 patients (1.9%) experienced recurrent thrombosis, 4 (0.97%) suffered a major bleeding event, and 3 (0.72%) suffered a minor bleeding event. There were no deaths related to thrombosis or bleeding. Four patients (0.97%) died from unrelated causes. Twenty-two (5.3%) patients experienced an INR > or =5.0 in the first 8 days of therapy, and none of these patients experienced a bleeding event. Eighty-four percent of patients achieved a therapeutic INR by day 5. In outpatients, a 10 mg nomogram results in timely achievement of a therapeutic INR with an acceptable incidence of bleeding and recurrent thromboembolism.