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Generic alendronate use among medicare beneficiaries: are part d data complete?

  1. Huifeng Yun1,3,*,
  2. Jeffrey R Curtis1,2,
  3. Kenneth Saag1,2,
  4. Meredith Kilgore3,
  5. Paul Muntner1,
  6. Wilson Smith1,
  7. Robert Matthews1,
  8. Nicole Wright1,
  9. Michael A. Morrisey3,
  10. Elizabeth Delzell1

Article first published online: 8 NOV 2012

DOI: 10.1002/pds.3361

Issue

Pharmacoepidemiology and Drug Safety

Pharmacoepidemiology and Drug Safety

Volume 22, Issue 1, pages 55–63, January 2013

Additional Information

How to Cite

Yun, H., Curtis, J. R., Saag, K., Kilgore, M., Muntner, P., Smith, W., Matthews, R., Wright, N., Morrisey, M. A. and Delzell, E. (2013), Generic alendronate use among medicare beneficiaries: are part d data complete?. Pharmacoepidem. Drug Safe., 22: 55–63. doi: 10.1002/pds.3361

Author Information

  1. 1

    Department of Epidemiology, University of Alabama at Birmingham, Birmingham, AL, USA

  2. 2

    Division of Clinical Immunology and Rheumatology, University of Alabama at Birmingham, Birmingham, AL, USA

  3. 3

    Department of Health Care Organization and Policy, University of Alabama at Birmingham, Birmingham, AL, USA

*H. Yun, Department of Epidemiology, Department of Health Care Organization and Polidy, School of Public Health, University of Alabama at Birmingham Birmingham, LHL 439, 1700 University Blvd, Birmingham, AL 35294, AL, USA. E-mail: yunn@uab.edu

Publication History

  1. Issue published online: 7 JAN 2013
  2. Article first published online: 8 NOV 2012
  3. Manuscript Revised: 26 SEP 2012
  4. Manuscript Accepted: 26 SEP 2012
  5. Manuscript Received: 22 MAY 2012

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Keywords:

  • generic drugs;
  • alendronate;
  • Medicare Part D;
  • medication adherence;
  • pharmacoepidemiology

ABSTRACT

Background

Generic alendronate was approved in the United States on February 6, 2008. Medicare beneficiaries might pay for generic alendronate out-of-pocket without having claims submitted, resulting in misclassification of generic alendronate use in Medicare data.

Objectives

To estimate the completeness of generic alendronate use in 2008 Medicare Part D data; to identify factors associated with staying on branded alendronate versus switching to a generic product.

Methods

We identified Medicare beneficiaries highly adherent (medication possession ratio ≥80%) with branded alendronate during 1/1/06–2/6/07 (“2007 cohort”) and during 1/1/07–2/6/08 (“2008 cohort”). The outcome was medication status at the end of follow-up (12/31/2007 or 12/31/2008), classified as continued branded alendronate, switched to generic alendronate, switched to another bisphosphonate or presumed discontinued bisphosphonate therapy. Cox regression estimated the hazard ratio (HR) for discontinuation in 2008 compared to 2007. Multinomial logistic regression identified factors associated with medication status for the 2008 cohort.

Results

Among 15 310 subjects using branded alendronate in the 2008 cohort, 81% switched to generic alendronate. The proportion presumably discontinuing bisphosphonate therapy was 8.9% in 2008 compared to 7.7% in the 2007 cohort (adjusted HR, 1.15; 95% confidence interval, 1.05, 1.26). Factors associated with staying on branded alendronate in 2008 were higher income, eligibility for a low income subsidy and use of Fosamax® plus vitamin D.

Conclusion

Evaluation of Medicare prescription drug data suggests that the amount of missing claims for generic alendronate in 2008 was not substantial, and misclassification of exposure in studies examining alendronate use post-generic product availability should be minimal. Copyright © 2012 John Wiley & Sons, Ltd.

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