Warfarin maintenance dosages in the very elderly

The effect of age on maintenance dosages among elderly patients with a stable International Normalized Ratio (INR) was studied.

The records of all patients monitored by an anticoagulation clinic between October 2000 and July 2002 were randomly selected for review. Data collection continued until at least 50 patients were enrolled in each of the following age groups: <75, 75-79, 80-84, and >/=85 years. To be included in the analysis, patients had to have been >50 years of age, had to have had a targeted INR of 2-3, and had to have had two consecutive INR values within the targeted range not more than 60 days apart.

A total of 532 patient charts were reviewed, and 253 met the criteria for inclusion in the study. The mean +/- S.D. age of the patients was 80.6 +/- 7.8 years (range, 55-98 years). Atrial fibrillation or flutter was the most common indication for treatment. The mean daily warfarin dose was significantly lower with increasing age; the mean +/- S.D. daily dose for patients younger than 75 years was 4.9 +/- 2.6 mg/day, while that for patients 85 years or older was 3.5 +/- 2.6 mg/day.

The warfarin dosage for maintenance therapy in elderly patients, especially those older than 75 years, appeared to be inversely related to age.