Lowering copayments: impact of simvastatin patent expiration on patient adherence.

OBJECTIVE: To assess the impact of a decrease in statin copayments on medication adherence and demand for statins. STUDY DESIGN: Quasi-experimental, pre/post design. METHODS: Patients in more than 700 health plans from June 2005 to May 2007 were evaluated. The intervention group (n = 13,319) and matched control group (n = 26,569) included patients who had at least 1 branded simvastatin or non-simvastatin statin purchase, respectively, before the simvastatin patent expired in June 2006. Intervention and control patients had to have purchased at least 1 generic simvastatin and non-simvastatin statin, respectively, after patent expiration. Intervention patients were matched to control patients up to 1:2 on incident statin use (yes/no) and pre-patent expiration copay (+/- $2). Adherence was calculated with the medication possession ratio (MPR). Adjusted and unadjusted changes in MPR were compared between groups. Elasticity of demand for statins was estimated. RESULTS: A small but statistically significant difference was observed between groups in the change in MPR (intervention = 0.52% adjusted mean increase, control = 2.02% adjusted mean decrease; adjusted P <.01). A marginally higher percentage of intervention patients (10.5%) compared with control patients (10.0%) increased their MPR from <80% in the preperiod to > or = 80% in the postperiod (adjusted P <.01). Elasticity of demand for statins was estimated at 0.02 and -0.02 for the copayment reduction categories of $0 to $5 and >$15, respectively. CONCLUSIONS: Decreasing statin copayments was associated with adherence increases. However, the overall increase in medication adherence was modest and its clinical significance uncertain.