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Incident User Cohorts for Assessing Medication Cost-Offsets

Authors

  • Bruce Stuart Ph.D.,

    Corresponding author
    1. Peter Lamy Center on Drug Therapy and Aging, Department of Pharmaceutical Health Services Research, University of Maryland School of Pharmacy, Baltimore, MD 21201
    • Address correspondence to Bruce Stuart, Ph.D., The Peter Lamy Center on Drug Therapy and Aging, Department of Pharmaceutical Health Services Research, University of Maryland School of Pharmacy, 220 Arch Street, Room 12-212, Baltimore, MD 21201; e-mail: bstuart@rx.umaryland.edu.

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  • F. Ellen Loh M.B.A., B.S.Pharm.,

    1. Department of Pharmaceutical Health Services Research, University of Maryland School of Pharmacy, Baltimore, MD
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  • Pamela Roberto M.P.P.,

    1. Pharmaceutical Research and Manufacturers of America, Washington, DC
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  • Laura Miller Ph.D.

    1. National Association of Chain Drug Stores, Arlington, VA
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Abstract

Objective

To develop and test incident drug user designs for assessing cost savings from statin use in diabetics.

Data Source

Random 5 percent sample of Medicare beneficiaries, 2006–2008.

Study Design

Seven-step incident user design to assess impact of statin initiation on subsequent Medicare spending: (1) unadjusted pre/post initiation test; (2) unadjusted difference-in-difference (DID) with comparison series; (3) adjusted DID; (4) propensity score (PS)-matched DID with static and dynamic baseline covariates; (5) PS-matched DID by drug adherence strata; (6) PS-matched DID for high adherers controlling for healthy adherer bias; and (7) replication for ACE-inhibitor/ARB initiators.

Data Collection/Extraction Methods

Subjects with prevalent diabetes and no statin use (January–June 2006) and statin initiation (July 2006–January 2008) compared to nonusers with a random “potential-initiation” month. Monthly Medicare spending tracked 24 months pre- and post-initiation.

Principal Findings

Statistically significant savings in Medicare spending were observed beginning 7 months post-initiation for statins and 13 months post-initiation for ACEIs/ARBs. However, these savings were only observed for adherent patients in steps 5 and 6.

Conclusions

Drug initiator designs are more robust to confounding than prevalent user designs in assessing cost-offsets from drug use but still require other adjustments and sensitivity analysis to ensure proper inference.

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