Warfarin started at 10 mg achieves therapeutic INR faster than 5 mg

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Warfarin started at 10 mg achieves therapeutic INR faster than 5 mg

J Fam Pract. 2003 September;52(9):664-688

By

Alan Cementina, MD

Eric A. Jackson, PharmD

BACKGROUND: Though not frequently undertaken by family physicians, the treatment of acute venous thromboembolism is now common in the outpatient setting. Patients are treated with a low-molecular-weight heparin, and warfarin is initiated within 24 hours.
POPULATION STUDIED: Researchers at 4 Canadian thrombosis clinics enrolled 201 outpatients with confirmed acute venous thromboembolism. Patients ranged in age from 18 to 98 years (mean, 55.5 years), 16% being older than 75 years. After randomization, baseline characteristics of both treatment groups were similar, although the 10-mg group included more men.
STUDY DESIGN AND VALIDITY: Subjects were randomly assigned to receive warfarin induction using either a modified, previously developed nomogram¹ starting with 5 mg on the 2 days (n=97) or a new nomogram starting with 10 mg on the first 2 days (n=104). Warfarin was started on the first day of treatment with subcutaneous low-molecular-weight heparin, which was continued for at least 5 days until a therapeutic INR was achieved. Subsequent doses of warfarin were determined from the respective nomograms. INR values were checked on days 3, 4, and 5 in all patients, although the 10-mg nomogram did not require an INR on day 4. Patients were followed for 90 days.
OUTCOMES MEASURED: The primary outcome was time in days to a therapeutic INR (>1.9). Secondary outcomes included the proportion of patients with an INR between 2.0 and 3.0 on day 5, total number of INR measurements, incidence of recurrent venous thromboembolism and major bleeding, and survival.
RESULTS: Patients in the 10-mg group achieved a therapeutic INR 1.4 days earlier than those in the 5-mg group (P<.001) and many more patients in the 10-mg group than in the 5-mg group achieved a therapeutic INR by day 5 (83% vs. 46%; P<.001; number needed to treat=2.7). As a result, fewer INR assessments were performed in the 10-mg group than in the 5-mg group (8.1 vs. 9.1; P=.04). No significant differences were found between the 2 groups in recurrent venous thrombotic events, major bleeding episodes (1 in each group), or survival over the 90 days of follow-up, though the study was not large enough to find a small difference in rates if one exists.

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Warfarin started at 10 mg achieves therapeutic INR faster than 5 mg

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