Anticoagulant management of atrial fibrillation: the influence of dosing algorithm and recall schedule on time in therapeutic range

BACKGROUND: The quality of anticoagulation management in atrial fibrillation patients is reflected by the concept of time spent in therapeutic range (TTR). In a primary care setting, the implementation of a dose nomogram could help increase the mean TTR among these patients.
OBJECTIVE: This study compares the influence of a dose algorithm with an integrated recall on TTR prior to standard care and after the implementation of the protocol.
PATIENTS AND METHODS: In a purposive sample of patients with AF, an uncontrolled 'before' and 'after' study design was utilized to measure the effects of the protocol on TTR. Demographic data, TTR levels, frequency of international normalized ratio (INR) within therapeutic range, clinician adherence to dose nomogram and warfarin dose changes were captured from consultations at the anticoagulation clinic.
RESULTS: A total of 152 patients with AF were entered into the final analysis. The increment in mean TTR in the 'after' intervention phase (2.9%) was not statistically significant (57.5-60.4%, P=0.252). The increase in the frequency of INR values within therapeutic range in the 'after' intervention phase was significant (50.0-56.0%, P<0.05) but with a very low effect size (r=0.04).
CONCLUSIONS: The implementation of a dose nomogram has the potential of reducing unnecessary dose changes for minor fluctuations in INR levels. The findings in this study needs to be confirmed in a future study involving other indications for anticoagulation, various regional primary care clinics and a larger population size.
KEYWORDS: Atrial fibrillation; TTR; dose nomogram; predictors; primary care; warfarin.
Study site: Klinik Kesihatan Seremban, Negeri Sembilan, Malaysia