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2012 HSR&D/QUERI National Conference Abstract

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2012 National Meeting

1078 — The Impact of Prescription Copayment Increases on Medication Adherence: Are There Racial Differences?

Wong ES, HSR&D Northwest Center for Outcomes Research in Older Adults, VAPSHCS; Maciejewski ML, Durham VAMC HSR&D Center of Excellence; Liu CF, HSR&D Northwest Center for Outcomes Research in Older Adults, VAPSHCS;

Objectives:
Previous studies have found that a system-wide increase in prescription copayments was associated with decreases in adherence to diabetes, hypertension, and hyperlipidemic medications. This study examines whether these effects differed by race.

Methods:
We used a retrospective pre-post cohort design to analyze 30-day adherence among Veterans diagnosed with diabetes, hypertension, or both at four Veterans Affairs (VA) medical centers. In February 2002, prescription copayments were increased from $2 to $7 for a 30-day supply. We compared changes in medication adherence in the near-post (12 months after copayment change) and the far-post (13-23 months after copayment change) periods to the pre-period (12 months prior). We used a difference-in-difference approach to compare changes in adherence between the non-exempt (Veterans required to pay copayments) and exempt (Veterans not required to pay copayments) groups. Propensity score matching was used to reduce potential biases due to covariate imbalance between the exempt and non-exempt groups. Regression models were fit using generalized estimating equations. We then compared the effect of the copayment increase for white and non-white Veterans.

Results:
After accounting for time trends in adherence, we found that the probability that Veterans were adherent decreased in the near-post period. The difference in the effect of the copayment increase between white and non-white Veterans was not statistically significant for diabetes (0.076, p = 0.142), hypertension (-0.006, p = 0.771), and hyperlipidemic (-0.024, p = 0.440) medications. The probability of adherence also decreased in the far-post period for both racial groups. The difference in the effect of the copayment increase between white and non-white Veterans in the far-post period was also not statistically significant for diabetes (0.046, p = 0.269), hypertension (-0.014, p = 0.612), and hyperlipidemic (-0.039, p = 0.265) medications.

Implications:
An increase in prescription copayments from $2 to $7 adversely impacted adherence to all medications, but did not disproportionately affect white and non-white Veterans.

Impacts:
Our findings did not identify racial differences in the adverse effect of increased cost sharing, despite previously documented racial disparities in adherence within VA. Further research is needed to determine if organizational factors designed to promote adherence helped reduce the impact of the copayment increase for all racial groups.


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