Comparison of an age adjusted warfarin loading protocol with empirical dosing and Fennerty's protocol

A warfarin loading protocol adjusting doses for age was compared to both Fennerty's protocol (Fenn) and empirical dosing (Emp).

Patients beginning warfarin were randomised to receive doses according to either the age adjusted (Age) protocol or Fenn. Data were retrospectively collected for patients who had begun warfarin in the previous six months to represent empirical dosing. The study was performed on inpatients being commenced on warfarin for the first time at two teaching hospitals.

Endpoints were time to reach a stable, therapeutic International Normalised Ratio (INR) between 2-3, the number of patients experiencing an INR > or =4 in the first week and the number of patients who had a dose held in the first week.

Thirty-five patients were assessed in the Age group, 28 in the Fenn group, and 123 patients for the Emp group. Patients using the Age protocol achieved a stable, therapeutic INR more rapidly than either the Fenn (p=0.003, log rank test) or Emp (p<0.001) group. The Age group had a lower proportion of patients experiencing an INR > or =4 in the first week (p<0.05) as well as a lower proportion having doses held in the first week (p<0.01). There were no differences between Emp and Fenn for any of the endpoints.

Adjustment of warfarin loading doses for age exhibits clear superiority over the use of Fenn or Emp. This becomes increasingly important as the average age of patients being warfarinised increases, with the recognition that atrial fibrillation requires anticoagulation. Fenn consistently overdosed elderly patients, especially those aged 80 years and older.