title: Effect of multiple pharmacy use on medication adherence and drug-drug interactions in older adults with Medicare Part D.
abstract: OBJECTIVE
  To assess the association between multiple pharmacy use and medication adherence and potential drug-drug interactions (DDIs) in older adults.
  
  
  METHODS
  Cross-sectional propensity score-weighted analysis.
  
  
  METHODS
  2009 claims data.
  
  
  METHODS
  A nationally representative sample of 926,956 Medicare Part D beneficiaries aged 65 and older continuously enrolled in fee-for-service Medicare and Part D that year who filled one or more prescriptions at a community retail or mail order pharmacy.
  
  
  METHODS
  Multiple pharmacy use was defined as concurrent (overlapping time periods) or sequential use (non-overlapping time periods) of ≥ 2 pharmacies in the year. Medication adherence was calculated using a proportion of days covered of 0.80 or greater for eight therapeutic categories (beta-blockers, renin angiotensin system antagonists, calcium channel blockers, statins, sulfonylureas, biguanides (metformin), thiazolidinediones, and dipeptidyl peptidase-IV inhibitors). Potential DDIs arising from use of certain drugs across a broad set of classes were defined as the concurrent filling of two interacting drugs.
  
  
  RESULTS
  Overall, 38.1% of the sample used multiple pharmacies. Those using multiple pharmacies (concurrently or sequentially) consistently had higher adjusted odds of nonadherence (ranging from 1.10 to 1.31, P < .001) across all chronic medication classes assessed after controlling for sociodemographic, health status, and access to care factors than single pharmacy users. The adjusted predicted probability of exposure to a DDI was also slightly higher for those using multiple pharmacies concurrently (3.6%) than for single pharmacy users (3.2%, adjusted odds ratio (AOR) = 1.11, 95% confidence interval (CI) = 1.08-1.15) but lower in individuals using multiple pharmacies sequentially (2.8%, AOR = 0.85, 95% CI = 0.81-0.91).
  
  
  CONCLUSIONS
  Filling prescriptions at multiple pharmacies was associated with lower medication adherence across multiple chronic medications and a small but statistically significant greater likelihood of DDIs in concurrent pharmacy users.
authors: Division of Geriatric Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
authors: Zachary A
authors: ZA
authors: Marcum
authors: Julia
authors: J
authors: Driessen
authors: Carolyn T
authors: CT
authors: Thorpe
authors: Walid F
authors: WF
authors: Gellad
authors: Julie M
authors: JM
authors: Donohue
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D004347:Drug Interactions; D005260:Female; D006801:Humans; D008297:Male; D054524:Medicare Part D; D010593:Pharmaceutical Services / Q000458:organization & administration*; D057216:Propensity Score; D012189:Retrospective Studies; D013997:Time Factors; D014481:United States; D016903:Drug Monitoring
keywords: Medicare; drug interactions; medication adherence; pharmacy