Research article

A test of financial incentives to improve warfarin adherence

Kevin G Volpp^1,2,3,4 , George Loewenstein^2,5 , Andrea B Troxel^2,6 , Jalpa Doshi^1,2,3,4 , Maureen Price⁶ , Mitchell Laskin⁷ and Stephen E Kimmel^2,3,6

¹Center for Health Equity Research & Promotion, Philadelphia Veterans Affairs Medical Center, Philadelphia, PA, USA

²Center for Health Incentives, Leonard Davis Institute of Health Economics, Philadelphia, PA, USA

³Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA, USA

⁴Department of Health Care Management, the Wharton School, University of Pennsylvania, Philadelphia, PA, USA

⁵Department of Social and Decision Sciences, Carnegie Mellon University, Pittsburgh, PA, USA

⁶Center for Clinical Epidemiology and Biostatistics and Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, PA, USA

⁷Department of Pharmacy Service, Hospital of the University of Pennsylvania, Philadelphia, PA, USA

author email corresponding author email

BMC Health Services Research 2008, 8:272doi:10.1186/1472-6963-8-272

Published:	23 December 2008

Abstract

Background

Sub-optimal adherence to warfarin places millions of patients at risk for stroke and bleeding complications each year. Novel methods are needed to improve adherence for warfarin. We conducted two pilot studies to determine whether a lottery-based daily financial incentive is feasible and improves warfarin adherence and anticoagulation control.

Methods

Volunteers from the University of Pennsylvania Anticoagulation Management Center who had taken warfarin for at least 3 months participated in either a pilot study with a lottery with a daily expected value of $5 (N = 10) or a daily expected value of $3 (N = 10). All subjects received use of an Informedix Med-eMonitor™ System with a daily reminder feature. If subjects opened up their pill compartments appropriately, they were entered into a daily lottery with a 1 in 5 chance of winning $10 and a 1 in 100 chance of winning $100 (pilot 1) or a 1 in 10 chance of winning $10 and a 1 in 100 chance of winning $100 (pilot 2). The primary study outcome was proportion of incorrect warfarin doses. The secondary outcome was proportion of INR measurements not within therapeutic range. Within-subject pre-post comparisons were done of INR measurements with comparisons with either historic means or within-subject comparisons of incorrect warfarin doses.

Results

In the first pilot, the percent of out-of-range INRs decreased from 35.0% to 12.2% during the intervention, before increasing to 42% post-intervention. The mean proportion of incorrect pills taken during the intervention was 2.3% incorrect pills, compared with a historic mean of 22% incorrect pill taking in this clinic population. Among the five subjects who also had MEMS cap adherence data from warfarin use in our prior study, mean incorrect pill taking decreased from 26% pre-pilot to 2.8% in the pilot. In the second pilot, the time out of INR range decreased from 65.0% to 40.4%, with the proportion of mean incorrect pill taking dropping to 1.6%.

Conclusion

A daily lottery-based financial incentive demonstrated the potential for significant improvements in missed doses of warfarin and time out of INR range. Further testing should be done of this approach to determine its effectiveness and potential application to both warfarin and other chronic medications.