title: Part D coverage gap and adherence to diabetes medications.
abstract: OBJECTIVE
  To evaluate the impact of Medicare Part D coverage gap (donut hole) on adherence to diabetes medications.
  
  
  METHODS
  Retrospective cohort analysis based on pharmacy claims data.
  
  
  METHODS
  The sample included 12,881 Medicare Part D beneficiaries with diabetes who entered the coverage gap in 2008. Sample patients had 3 different levels of coverage in the donut hole: no coverage, generic drug coverage only, and both generic and brand-name drug coverage. Adherence was measured by the proportion of days covered. We used a difference-in-difference model to evaluate the effect of coverage gap on adherence.
  
  
  RESULTS
  In the donut hole, the average copayment for diabetes medications increased substantially for beneficiaries with no coverage and beneficiaries with generic drug coverage only, whereas the average copayment for beneficiaries with both generic and brand-name medication coverage declined slightly. Compared with beneficiaries with full coverage of both generic and brand-name drugs, beneficiaries with no coverage (odds ratio[OR] = 0.617, P <.0001, 95% confidence interval [CI] = 0.523, 0.728) and beneficiaries with generic drug coverage only (OR = 0.702, P <.0001, 95% CI = 0.604, 0.816) were significantly less likely to be adherent after entering the donut hole. The difference between having generic coverage and no coverage was not significant (P = .1586).
  
  
  CONCLUSIONS
  The coverage gap in the Medicare Part D program has a significant negative impact on medication adherence among beneficiaries with diabetes. Availability of brand-name drug coverage in the donut hole is critical to adherence to diabetes medications.
authors.affiliation: School of Policy, Planning, and Development, University of Southern California, Los Angeles, CA, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Gu
authors.forename: Feng
authors.initials: F
authors.lastname: Zeng
authors.forename: Bimal V
authors.initials: BV
authors.lastname: Patel
authors.forename: Louis C
authors.initials: LC
authors.lastname: Tripoli
mesh_terms: D000368:Aged; D015331:Cohort Studies; D016001:Confidence Intervals; D003920:Diabetes Mellitus / Q000188:drug therapy* / Q000191:economics; D005260:Female; D052216:Glucagon-Like Peptide 1 / Q000191:economics / Q000627:therapeutic use; D006297:Health Services Accessibility; D006801:Humans; D007004:Hypoglycemic Agents / Q000191:economics / Q000627:therapeutic use; D054795:Incretins / Q000191:economics / Q000627:therapeutic use; D007328:Insulin / Q000191:economics / Q000627:therapeutic use; D007345:Insurance Claim Review; D019458:Insurance Coverage / Q000191:economics / Q000706:statistics & numerical data*; D008297:Male; D054524:Medicare Part D / Q000191:economics / Q000706:statistics & numerical data*; D008687:Metformin / Q000191:economics / Q000627:therapeutic use; D016017:Odds Ratio; D012189:Retrospective Studies; D013453:Sulfonylurea Compounds / Q000191:economics / Q000627:therapeutic use; D045162:Thiazolidinediones / Q000191:economics / Q000627:therapeutic use; D014481:United States; D016903:Drug Monitoring
chemical_list: D007004:Hypoglycemic Agents; D054795:Incretins; D007328:Insulin; D013453:Sulfonylurea Compounds; D045162:Thiazolidinediones; D052216:Glucagon-Like Peptide 1; D008687:Metformin