Lowering copayments: impact of simvastatin patent expiration on patient adherence

To assess the impact of a decrease in statin copayments on medication adherence and demand for statins.Quasi-experimental, pre/post design.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.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 from80% in the preperiod toor = 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.Decreasing statin copayments was associated with adherence increases. However, the overall increase in medication adherence was modest and its clinical significance uncertain.