Time to Stable Therapeutic Range on Initiation of Warfarin as an Indicator of Control

Abstract

Objectives: Warfarin remains widely used with a time in therapeutic range (TiTR) above 65% recommended for best outcomes. Patients not achieving or maintaining this warfarin control may be better suited to alternate anticoagulants. Despite this, there is limited data defining a suitable trial time in patients initiating warfarin therapy, therefore the aim of this study was to determine the mean time to stable therapeutic range (TtSTR). Materials and Methods: Retrospective data was collected for patients with atrial fibrillation enrolled in a dedicated warfarin program at a private pathology practice within 7 days of warfarin initiation. TiTR at specified timepoints was calculated and median TtSTR determined as defined by TiTR ≥ 65% over three months. Comparisons were made of populations with TtSTR above or below the median. Results: The 566 patients included in the study had a mean TiTR of 64.9±16.5% at month three and median TtSTR of six months. Patients with TtSTR≤6 months achieved a mean TiTR of 68.9±12.8% at month two and maintained a TiTR over 75% from month 3 to 24. Patients with a TtSTR>6 months obtained a TiTR of 66.4±10.6% at month nine and continued to achieve lower TiTR throughout the 24 months study period. Conclusions: A majority of patients can achieve a stable TiTR above 65% within six months so review at six to nine months is likely to be a good indicator of warfarin control and to determine if patients should continue warfarin or switch to alternate anticoagulant therapy.