Trends in Proportion of Medicare Part D Claims Subject to 340B Discounts, 2013-2020

IMPORTANCE: Despite controversy surrounding the 340B program, no study has analyzed trends in the proportion of Medicare Part D pharmacy claims eligible for 340B discounts. OBJECTIVE: To describe trends in the proportion of Medicare Part D claims that are prescribed by 340B-affiliated clinicians and filled in 340B pharmacies. DESIGN AND SETTING: This longitudinal, retrospective cohort study included 2013 to 2020 claims data from a 5% random sample of Medicare Part D beneficiaries from the Centers for Medicare & Medicaid Services and 6292 nine-digit national drug codes that were used by at least 1000 Part D beneficiaries in a given year. Data analysis was completed from November 2022 to April 2023. MAIN OUTCOMES AND MEASURES: For each drug and year, there were 3 outcomes: (1) proportion of total Part D claims that were prescribed by a 340B-affiliated clinician; (2) proportion of claims prescribed by a 340B-affiliated clinician that were filled in a 340B pharmacy; and (3) proportion of total Part D claims under the 340B program (ie, prescribed by a 340B-affiliated clinician and filled in a 340B pharmacy). RESULTS: The proportion of prescriptions written by a 340B-affiliated clinician doubled from 9.4% in 2013 to 19.3% in 2020. The capture of 340B prescriptions by 340B pharmacies, defined as the proportion of claims prescribed by 340B-affiliated clinicians that were filled by 340B pharmacies, increased from 18.4% in 2013 to 49.9% in 2020. As a result, the total proportion of 340B claims in Part D increased from 1.7% in 2013 to 9.6% in 2020. Rates of 340B prescribing and capture increased consistently across therapeutic classes. In 2020, the antiviral therapeutic class was the class with the largest proportion of 340B claims (16.1%), followed by targeted antineoplastics (15.7%). CONCLUSIONS AND RELEVANCE: This cohort study demonstrated that from 2013 to 2020, the share of Medicare Part D claims prescribed by a 340B-affiliated clinician increased; however, the rate at which 340B-eligible prescriptions were filled at 340B pharmacies increased at a faster rate, driving the overall increase in 340B claims. Despite these trends, only half of 340B-eligible prescriptions were subject to the 340B discount in 2020.