Randomized trial of lottery-based incentives to improve warfarin adherence

Abstract

Background: Poor adherence to medications is a major cause of morbidity and inadequate drug effectiveness. Efforts to improve adherence have typically been either ineffective or too complex to implement in clinical practice. Lottery-based incentive interventions could be a scalable approach to improving adherence.

Methods: This was a randomized, controlled clinical trial of a daily lottery-based incentive in patients on warfarin stratified by baseline international normalized ratio (INR). The trial randomized 100 patients to either a lottery-based incentive or no lottery intervention. Main outcome was out-of-range INRs.

Results: Over 6 months, the overall percentage of out-of-range INRs did not differ between the 2 arms (mean 23.0% in lottery arm and 25.9% in control arm, adjusted odds ratio [OR] 0.93, 95% CI 0.62-1.41). However, among the a priori subgroup with a baseline INR below therapeutic range, there was a significant reduction in out-of-range INR in the lottery arm versus the control arm (adjusted OR 0.39, 95% CI 0.25-0.62), whereas there was no such effect among those with therapeutic INRs at baseline (adjusted OR 1.26, 95% CI, 0.76-2.09, P value for interaction = .0016). Among those with low INR at baseline, there was a nonsignificant 49% reduction in the odds of nonadherence with the intervention (OR 0.51, 95% CI 0.23-1.14).

Conclusions: Although a lottery-based intervention was not associated with a significant improvement in anticoagulation control among all study participants, it improved control among an a priori group of patients at higher risk for poor adherence.

Trial registration: ClinicalTrials.gov NCT00904982.

Figure 1

Patient flowchart.

Figure 2

A, Out-of-range INRs by study arm and a priori subgroup. Predictive probability of INR out of range. Primary outcome of out-of-range INRs by study arm and a priori subgroups of those with INR below range and INR within range at baseline. Results are presented as predicted probabilities from GEE logistic regression models. B, Nonadherence by study arm and a priori subgroup. Predictive probability of nonadherence. Secondary outcome of adherence by study arm and a priori subgroups of those with INR below range and INR within range at baseline. Results are presented as predicted probabilities from GEE logistic regression models.