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Evaluation of warfarin initiation regimens in elderly inpatients
M B O'Connell1, P R Kowal, C J Allivato
1Department of Experimental and Clinical Pharmacology, College of Pharmacy, University of Minnesota, Minneapolis 55455-0353, USA.
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.