Evaluation of warfarin initiation regimens in elderly inpatients

Study Objective. To compare initial warfarin doses of 5 mg or below and doses above 5 mg in hospitalized elderly, Design. Retrospective review of charts identified from computerized pharmacy records. Setting. County teaching hospital. Patients. Inpatients aged 65 years or older receiving at least three warfarin doses. Intervention. We measured the time to first international normalized ratio(INR) of 2.0 or greater, bleeding complications, number of warfarin doses held, and vitamin K use. Measurements and Main Results. The average initial low dose (33 patients) was 4.8 ± 0.8 mg and the average initial high dose (40 patients) was 9.0 ± 1.2 mg. The mean time to first INR of 2.0 or greater was similar, 3.4 and 3.0 days, respectively (p=0.38). The low-dose group had fewer bleeds (7 vs 13, p=0.28) and doses held (11 vs 18 patients, p=0.27, 30 vs 50 doses). Four patients in each group received vitamin K (p=0.8). Forty-four percent of patients with an INR of 4 or above and 48% of patients who had a dose held were on a long-term drug or had a new drug added that could cause a major drug interaction with warfarin. Conclusion. In this pilot study, hospitalized elderly who received a low versus high initial dose of warfarin achieved therapeutic INRs in a similar time and had lower but not significantly different safety outcomes.