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

Aim: A warfarin loading protocol adjusting doses for age was compared to bo th Fennerty's protocol (Fenn) and empirical dosing (Emp). Methods: Patients beginning warfarin were randomised to receive doses accor ding to either the age adjusted (Age) protocol or Fenn. Data were retrospec tively collected for patients who had begun warfarin in the previous six mo nths to represent empirical dosing. The study was performed on inpatients b eing commenced on warfarin for the first time at two teaching hospitals. Main outcome measures: Endpoints were time to reach a stable, therapeutic I nternational Normalised Ratio (INR) between 2-3, the number of patients exp eriencing an INR greater than or equal to 4 in the first week and the numbe r of patients who had a dose held in the first week. Results: Thirty-five patients were assessed in the Age group, 28 in the Fen n group, and 123 patients for the Emp group. Patients using the Age protoco l 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 prop ortion of patients experiencing an INR 24 in the first week (p<0.05) as wel l 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. Conclusion: Adjustment of warfarin loading doses for age exhibits clear sup eriority over the use of Fenn or Emp. This becomes increasingly important a s the average age of patients being warfarinised increases, with the recogn ition that atrial fibrillation requires anticoagulation. Fenn consistently overdosed elderly patients, especially those aged 80 years and older.