Influence Of Cost Sharing Differentials On Therapeutic Substitution And Medication Adherence: The Story Of Statins In 2006

  • Li P
  • Schwartz S
  • Doshi J
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Objectives: The availability of enhanced Medicare Part D plans with generic-only coverage during the coverage gap (i.e. donut hole) and the genericization of pravas- tatin and simvastatin in early 2006, respectively, created a unique opportunity to examine how patient cost-sharing differentials for brand-name and generic drugs impact therapeutic substitution and medication adherence with statins. Methods: Using the 2006 5% Medicare files we identified continuous fee-for-service Part D covered patients with hyperlipidemia (ICD-9-CM 272.0-272.4) using the brandname statins (atorvastatin or rosuvastatin) between 1/1/2006 and 3/31/2006. The quasi-experimental study examined changes in outcomes across the pre- (prior to coverage gap) and post- (during coverage gap) periods for non-low income subsidy (non-LIS) patients with generic-only coverage in gap who faced substantial increases in brand-name statin cost sharing ($28 to $82 per 30-day supply) but no changes in generic cost-sharing from the pre- to post-period compared to a control group of LIS patients who faced no changes in brand-name ($3) or generic ($1) cost-sharing in the pre- and post-periods. The two groups were propensity-score matched on sociodemographics and clinical characteristics. Difference-in-difference regressions were used to examine impact on use of brand-name statins, generic statins, and overall any statin use. In addition, overall adherence (PDC> 0.80) to and discontinuation (30-day gap) of statins was also examined. Results: Compared to LIS patients, non-LIS patients had a larger decline in brand-name statin use (-0.24 30-day-supply/ month, p< 0.001), smaller increase in generic statin use (+0.06 30-day-supply/ month, p< 0.001), and hence, an overall drop in any statin use (-0.18 30-day-supply/ month, p< 0.001). Correspondingly, a decrease in adherence (OR: 0.81,p< 0.001) and increase in discontinuation (OR: 1.62,p< 0.001) on any statins was observed in non- LIS patients relative to LIS patients. Conclusions: A substantial brand/generic cost-sharing differential was associated with therapeutic substitution of brandname statins with generic statins; however, it also resulted in declines in adherence and increases in discontinuation of statins.




Li, P., Schwartz, S. J., & Doshi, J. A. (2015). Influence Of Cost Sharing Differentials On Therapeutic Substitution And Medication Adherence: The Story Of Statins In 2006. Value in Health, 18(3), A147–A148.

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