Generic entry of aromatase inhibitors and pharmaceutical access: Initiation of hormonal therapy, timeliness of initiation, and drug choice

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BACKGROUND: The trade-offs between innovation and pharmaceutical access are central to the policy debate on drug pricing. High prices may limit access, result in medication underuse, and negatively affect outcomes. Generic drugs make treatments more affordable. Prior research measured access as utilization without a defined population that should receive certain drugs, it is unknown whether generic entry reduces underuse and thus improves access.

OBJECTIVES: To measure changes in access (use, timeliness) with the introduction of three generic aromatase inhibitors (AIs, oral breast cancer drugs) between June 2010 and June 2011.

METHODS: This population-based study included 93,650 older (65+) women diagnosed with hormone receptor-positive breast cancer between 2007 and 2013 in the Surveillance, Epidemiology and End Results-Medicare linked database. We examined changes in access with generic entry for initiation of any adjuvant hormonal therapy drug (AIs or tamoxifen) within one year of diagnosis, time from diagnosis to initiation, and choice of initial therapy.

RESULTS: Among 93,650 newly diagnosed breast cancer cases, 67,372 initiated one of the four drugs. With generic entry, initiation rates increased from 69.5% to 74.3%, but non-initiation remained high (up to 25.7%). After controlling for demographics, clinical factors, and insurance coverage, the probability of initiation increased by 4.6 percentage points (P < 0.001, 95%CI: [4.1,5.2]) after generic entry. With generic entry, estimated time to initiation decreased by 0.3 months (P < 0.001, 95%CI: [0.2,0.3]) from 4.1 months, and the probability of choosing AIs over tamoxifen increased by 5.9 percentage points (P < 0.001, 95%CI: [5.3,6.5]). Patterns did not substantially differ by level of cost-sharing.

CONCLUSIONS: Generic entry of AIs was associated with increased probability of receiving recommended treatments, timeliness of treatment, and the probability of receiving clinically preferred treatments. Price changes with generic entry only partially explained these improvements. High non-initiation rates after generic entry suggest prices are not the sole determinant of access.

Original languageEnglish (US)
Pages (from-to)1588-1595
Number of pages8
JournalResearch in Social and Administrative Pharmacy
Issue number9
StatePublished - Sep 2021

Bibliographical note

Publisher Copyright:
© 2020 Elsevier Inc.


  • Access
  • Aromatase inhibitors
  • Breast cancer
  • Generic entry
  • Medicare
  • Tamoxifen
  • United States
  • Humans
  • Tamoxifen/therapeutic use
  • Aromatase Inhibitors/therapeutic use
  • Female
  • Aged
  • Breast Neoplasms/drug therapy
  • Drugs, Generic

PubMed: MeSH publication types

  • Journal Article


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