Patient co-payment and adherence to statins: a review and case studies

This study aims to review the international literature about whether there is an association between co-payment and statin adherence, and to present case studies to illustrate the impact of a reduction in patient co-payment associated with generic drugs on improving therapy adherence.

Studies that examined the impact of patient co-payment on statin adherence were identified in PubMed, Cochrane Central Register of Controlled Trials and EconLit up to January 2013. A standardized data extraction form was completed for each included study, collecting information about country, sample, setting, adherence measure, design, results about the impact of co-payment on statin adherence, and methodological quality. Two cases from the outpatient clinic of one the authors (PRS) were added.

The literature supported a statistically significant negative association between co-payment and statin adherence. This association appeared to be influenced by the absolute level of co-payments, the size of the co-payment change, whether co-payment increases or decreases, the time horizon over which the impact of a co-payment change is examined, the type of drug for which co-payment changes (e.g. generic or branded drug), the availability of alternative drugs and switching behaviour. Two case studies illustrated that cost issues are important to patients and that patient adherence to statin therapy improved following a switch to generic statins.

Current studies have demonstrated that statin adherence is influenced by co-payment and a range of patient, physician and pharmacy characteristics. Nevertheless, the power of these models to explain the variation in adherence remains limited.