Journal of General Internal Medicine

, Volume 28, Issue 7, pp 876–885

Cost Sharing and Decreased Branded Oral Anti-Diabetic Medication Adherence Among Elderly Part D Medicare Beneficiaries

  • Naomi C. Sacks
  • James F. BurgessJr.
  • Howard J. Cabral
  • Steven D. Pizer
  • Marie E. McDonnell
Original Research



Although the Medicare Part D coverage gap phase-out should reduce cost-related nonadherence (CRN) among seniors with diabetes, preferential generic prescribing may have already decreased CRN, while smaller numbers of patients using more costly branded oral anti-diabetic (OAD) medications remain vulnerable to CRN.


To estimate the effects of cost sharing in the Part D standard (non-LIS) benefit on adherence to different OAD classes, comparing two classes dominated by inexpensive generic medications and two by more costly branded medications.


Retrospective cohort study using dispensed prescription data for elderly non-LIS (N = 81,047) and LIS (low-income subsidy) (N = 150,359) beneficiaries using same class OAD(s) in 2008 and 2009. Logistic regression modeled non-LIS likelihood; LIS and non-LIS patients matched using propensity outcome (N = 38,054). Logistic regression, controlling for demographic and health status characteristics, modeled effects of non-LIS coverage on 2009 OAD class adherence.


Main outcome measures were within-class OAD coverage year adherence, with patients considered adherent when days supplied to calendar days ratio at least 0.8.


Non-LIS patients had 0.52 and 0.57 times the odds of branded-only DPP-4 Inhibitor (N = 1,812; 95 % CI: 0.43, 0.63; P < 0.001) and Thiazolidinedione (TZD) (N = 6,290; 95 % CI: 0.52, 0.63; P < 0.001) adherence. Most patients (N = 32,510; 82 %) used OADs in primarily generic classes, where we found no significant (Biguanides; N = 21,377) or small differences (Sulfonylureas/Glinides [N = 19,240; OR: 0.91; 95 % CI: 0.86, 0.97; P = 0.002]) in adherence odds. Crude adherence rates were sub-optimal when CRN was not a factor (Non-LIS/LIS: Biguanides: 65 %/65 %; Sulfonylureas/Glinides: 66 %/68 %; LIS: DPP-4 Inhibitors: 66 %; TZDs: 67 %).


Gap elimination would not affect generic, but should reduce branded OAD CRN. Branded copayments may continue to lead to CRN. Policy initiatives and benefit changes targeting both cost deterrents for patients with more complex disease and non-cost generic OAD underuse are recommended.


Medicare medication adherence diabetes Part D coverage gap 

Supplementary material

11606_2013_2342_MOESM1_ESM.doc (36 kb)
Appendix ATimeframes for Variables Used in Analyses (DOC 36 kb)
11606_2013_2342_MOESM2_ESM.doc (52 kb)
Appendix BEstimates of Effects of Non-LIS Coverage and All Independent Variables on Adherence by OAD Class. (Unmatched Patient Sample) (DOC 52 kb)
11606_2013_2342_MOESM3_ESM.doc (50 kb)
Appendix CMatched Analytic Samples (4 significant digit matching) (DOC 50 kb)
11606_2013_2342_MOESM4_ESM.doc (152 kb)
Appendix DEffects of Non-LIS Coverage on Adherence (4-digit Matched Sample) (DOC 152 kb)

Copyright information

© Society of General Internal Medicine 2013

Authors and Affiliations

  • Naomi C. Sacks
    • 2
    • 3
  • James F. BurgessJr.
    • 1
    • 2
  • Howard J. Cabral
    • 4
  • Steven D. Pizer
    • 2
    • 7
  • Marie E. McDonnell
    • 5
    • 6
  1. 1.Center for Organization, Leadership and Management ResearchVA BostonBostonUSA
  2. 2.Department of Health Policy and ManagementBoston University School of Public HealthBostonUSA
  3. 3.IMS Health Payer SolutionsWalthamUSA
  4. 4.Department of BiostatisticsBoston University School of Public HealthBostonUSA
  5. 5.Department of Medicine, Section of EndocrinologyBoston Medical CenterBostonUSA
  6. 6.Department of MedicineBoston University School of MedicineBostonUSA
  7. 7.Health Care Financing and EconomicsVA Boston Healthcare SystemBostonUSA

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