Association Between Patient-Reported Medication Adherence and Anticoagulation Control

Abstract

Background: The prevention of thromboembolism events remains challenging in cases of poor medication adherence. Unfortunately, clinical prediction of future adherence has been suboptimal. The objective of this study was to examine the correlation between 2 measures of real-time, self-reported adherence and anticoagulation control.

Methods: The IN-RANGE2 cohort recruited patients initiating warfarin therapy in 3 urban anticoagulation clinics. At each study visit, participants reported adherence using a 100-point visual analogue scale (VAS, marking percentage of pills taken since prior visit on a linear scale) and 7-day recall of pill-taking behavior. Anticoagulation control was measured by between-visit percent time in international normalized ratio range (BVTR), dichotomized at the cohort median. The longitudinal association between adherence and anticoagulation control was estimated using generalized estimating equations, controlling for clinical and demographic characteristics, prior BVTR, and warfarin dose changes.

Results: Among 598 participants with 3204 (median 4) visits, the median BVTR was 36.8% (interquartile range 0%-73.9%). Participants reported ≤80% adherence in 182 visits (5.7%) and missed pills in the past 7 days in 377 visits (11.8%). Multivariable regression analysis found poorer anticoagulation control (BVTR <36.8%) in those with a VAS ≤80% (odds ratio 1.89; 95% confidence interval, 1.12-3.18; P = .02) and self-reported change in adherence since last visit (odds ratio 1.55; 95% confidence interval, 1.20-2.01; P = .001).

Conclusion: Self-reported VAS medication adherence at a clinic visit and changes in reported adherence since the last visit are independently associated with BVTR. Clinicians may gain additional insight into patients' medication adherence by incorporating this information into patient management.

Keywords: Anticoagulation; Medication adherence; Self-report; Visual analogue scale; Warfarin.

Figure 1. Conceptual Framework

Poor medication adherence is strongly associated with poor anticoagulation control which places patients at increased risk of hemorrhagic and thromboembolic events. A challenge in addressing poor medication adherence has been to readily identify patients with poor adherence in order to provide them with additional resources and targeted interventions. Previous studies have found prediction models of future adherence to be suboptimal, and objective measurement, through electronic pill monitoring to be accurate but impractical in routine clinical practice. Our study’s aim (dashed box) was to analyze the association between two quick and easily implemented self-reported adherence measurements, a visual analogue scale and change in 7-day pill recall, an anticoagulation control.