Evaluating the Effects of Pioneer Accountable Care Organizations on Medicare Part D Drug Spending and Utilization

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The improvement of medication use is a critical mechanism that accountable care organization (ACO) could use to save overall costs. Currently pharmaceutical spending is not part of the calculation for ACO-shared savings and risks. Thus, ACO providers may have strong incentives to prescribe more medications hoping to avoid expensive downstream medical costs.


We designed a quasinatural experiment study to evaluate the effects of Pioneer ACOs on Medicare Part D spending and utilization. Medicare fee-for-service beneficiaries with Part D drug coverage who were aligned to a Pioneer ACO were compared with a random 5% sample of non-ACO beneficiaries. Outcomes included changes in Part D spending, number of prescription fills, percent of brand medications, and total Part A and B medical spending. We utilized a generalized linear model with a difference-in-differences approach to estimate 2011–2012 changes in these outcomes among beneficiaries aligned with Pioneer ACOs, adjusting for all beneficiary-level demographics, income and insurance status, clinical characteristics, and regional fixed effects.


Being in an ACO did not significantly affect Part D spending (−$23.52; P=0.19), total prescriptions filled (−0.12; P=0.27), and the percent of claims for brand-name drugs (0.06%; P=0.23). The ACO group was associated with savings in Parts A and B spending of $345 (P<0.0001) per person per year.


We found that beneficiaries aligned to Pioneer ACOs were not associated with changes in pharmaceutical spending and use, but were associated with savings in Parts A and B spending in 2012.

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