Association of Changes in Medication Use and Adherence With Accountable Care Organization Exposure in Patients With Cardiovascular Disease or Diabetes

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Many of the quality measures used to assess accountable care organization (ACO) performance in the Medicare Shared Savings Program (MSSP) focus on disease control and medication use among patients with cardiovascular disease and diabetes. To date, the association between participation in the MSSP by provider organizations and medication use or adherence among their patients with cardiovascular disease or diabetes has not been described.


To assess the association between exposure to the MSSP and changes in the use of and adherence to common antihypertensive, lipid-lowering, and hypoglycemic medications.

Design, Setting, and Participants

Fee-for-service Medicare claims from January 1, 2009, to December 31, 2014, were used to conduct difference-in-differences comparisons of changes for ACO-attributed beneficiaries from before the start of ACO contracts to 2014 with concurrent changes for beneficiaries attributed to local non-ACO providers (control group). A random 20% sample of Medicare beneficiaries contributing 4 482 168 to 10 849 224 beneficiary-years for analysis from 2009 to 2014, depending on the drug class, was examined. Differential changes were estimated separately for cohorts of ACOs entering the MSSP in 2012, 2013, and 2014. Data analysis was conducted from November 1, 2016, to April 5, 2017.


Patient attribution to an ACO after entry into the MSSP.

Main Outcomes and Measures

Any use (at least 1 prescription fill) and proportion of days covered (PDC), a standard claims-based measure of adherence, assessed for each of 6 drug classes: statins, angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers, β-blockers, thiazide diuretics, calcium channel blockers, and metformin.


Differences in patient characteristics between the MSSP and control group were generally small after geographic adjustment and changed minimally from the precontract period to 2014. There were no significant differential changes in medication use from the precontract period to 2014 for any cohort of MSSP ACOs in any drug class, except for a slight differential increase in the use of thiazides among beneficiaries with hypertension in the 2013 entry cohort (adjusted differential change, 0.5 percentage point; 95% CI, 0.1-0.8 percentage points; or 1.5% of the overall percentage using thiazides [33.4%], P = .01). Similarly, there were no significant differential changes in PDC among beneficiaries with at least 1 prescription fill, except for slight differential increases in the PDC for β-blockers in the 2012 entry cohort (adjusted differential change, 0.3 percentage point; 95% CI, 0.1-0.5 percentage points; or 0.4% of the mean PDC [82.3%], P = .003) and for metformin in the 2012 and 2013 cohorts (adjusted differential change, 0.5 percentage point; 95% CI, 0.1-0.9 percentage points; or 0.6% of the mean PDC [78.2%], P = .01 for both).

Conclusions and Relevance

Exposure to the MSSP has not been associated with meaningful changes in medication use or adherence among patients with cardiovascular disease and diabetes.

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