title: Entering and exiting the Medicare part D coverage gap: role of comorbidities and demographics.
abstract: BACKGROUND
  Some Medicare Part D enrollees whose drug expenditures exceed a threshold enter a coverage gap with full cost-sharing, increasing their risk for reduced adherence and adverse outcomes.
  
  
  OBJECTIVE
  To examine comorbidities and demographic characteristics associated with gap entry and exit.
  
  
  METHODS
  We linked 2005-2006 pharmacy, outpatient, and inpatient claims to enrollment and Census data. We used logistic regression to estimate associations of 2006 gap entry and exit with 2005 medical comorbidities, demographics, and Census block characteristics. We expressed all results as predicted percentages.
  
  
  METHODS
  287,713 patients without gap coverage, continuously enrolled in a Medicare Advantage Part D (MAPD) plan serving eight states. Patients who received a low-income subsidy, could not be geocoded, or had no 2006 drug fills were excluded.
  
  
  RESULTS
  Of enrollees, 15.9% entered the gap, 2.6% within the first 180 days; among gap enterers, only 6.7% exited again. Gap entry was significantly associated with female gender and all comorbidities, particularly dementia (39.5% gap entry rate) and diabetes (28.0%). Among dementia patients entering the gap, anti-dementia drugs (donepezil, memantine, rivastigmine, and galantamine) and atypical antipsychotic medications (risperidone, quetiapine, and olanzapine) together accounted for 40% of pre-gap expenditures. Among diabetic patients, rosiglitazone accounted for 7.2% of pre-gap expenditures. Having dementia was associated with twice the risk of gap exit.
  
  
  CONCLUSIONS
  Certain chronically ill MAPD enrollees are at high risk of gap entry and exposure to unsubsidized medication costs. Clinically vulnerable populations should be counseled on how to best manage costs through drug substitution or discontinuation of specific, non-essential medications.
authors.affiliation: Division of General Internal Medicine and Health Services Research, Department of Medicine, David Geffen School of Medicine at UCLA, 911 Broxton Plaza, Los Angeles, CA 90024, USA. settner@mednet.ucla.edu
authors.forename: Susan L
authors.initials: SL
authors.lastname: Ettner
authors.forename: Neil
authors.initials: N
authors.lastname: Steers
authors.forename: O Kenrik
authors.initials: OK
authors.lastname: Duru
authors.forename: Norman
authors.initials: N
authors.lastname: Turk
authors.forename: Elaine
authors.initials: E
authors.lastname: Quiter
authors.forename: Julie
authors.initials: J
authors.lastname: Schmittdiel
authors.forename: Carol M
authors.initials: CM
authors.lastname: Mangione
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002908:Chronic Disease / Q000188:drug therapy / Q000191:economics*; D015897:Comorbidity; D003710:Demography; D005260:Female; D005382:Financing, Personal; D005102:Health Expenditures; D006801:Humans; D019458:Insurance Coverage / Q000706:statistics & numerical data*; D016015:Logistic Models; D008297:Male; D054524:Medicare Part D / Q000706:statistics & numerical data*; D014481:United States