Spending on and Use of Clinician-Administered Drugs in Medicare.

Importance: Medicare Part B drug expenditures have increased in recent years. This trend is likely to persist given the increased use and availability of biologics. Objectives: To assess the extent to which Medicare Part B spending growth was associated with changes in price vs quantity, and how these trends interacted with entry of new drugs into the marketplace. Design, Setting, and Participants: This cross-sectional study quantified the degree of spending concentration and the association between price and use of Part B drugs among fee-for-service Medicare beneficiaries. Data on use and spending for separately payable Part B drugs were included. Source data were aggregated to the drug-year level and reported from 2016 to 2020. Descriptive decomposition and index analyses quantified the relative association of price and use changes separately for existing single-source drugs, existing drugs that faced competition, and new drugs that entered the market. Data analysis was performed from June to December 2022. Main Outcomes and Measures: Part B drug spending by the fee-for-service Medicare program and beneficiaries, as well as use, defined as dosage units and beneficiaries using the drugs. Results: The study included 535 unique Part B drug products. From 2016 to 2020, 15 or fewer products comprised half of all Part B drug expenditures. The set of 7 drugs that comprised the top 25% of spending was very consistent over time, and all were biologics. Part B drug products that cost $1.85 or less per administration accounted for more than half of the doses administered in 2020. Spending on Part B drugs increased by $15 billion from 2016 to 2020. The entry of new, nonbiosimilar drugs during this period accounted for $12 billion of this increased spending (80%), while shifts in use and price increases among existing single-source brand drugs accounted for the remaining increase in spending. Part B spending decreased among the subset of existing drugs facing generic or biosimilar competition. Among single-source drugs on the market in 2016, the index that varied dosage units exceeded the index that varied price in all years, confirming that changes in use were associated more with spending growth for those drugs. Conclusions and Relevance: In this cross-sectional study of Medicare Part B drug expenditures, spending was found to be concentrated among a small number of drugs. The entry of new products was a key factor associated with recent increases in Part B drug spending. These findings suggest that policies targeting top-selling drugs may have greater potential to curb Part B drug spending than those targeting price growth.