“Spending per dosage unit” is the metric behind most drug-price comparisons in the Medicare Part D data, but it is widely misunderstood. Here is exactly how it works.
The formula
Spending per dosage unit = Total spending ÷ Total dosage units
A dosage unit is one billing unit of the drug — a single pill, tablet, capsule, milliliter or gram. CMS sums all units dispensed across every claim in the year, then divides total spending by that count. Because a drug can come in several strengths and pack sizes, the result is a volume-weighted average.
Worked example: Eliquis
Eliquis had about $18.3B in total Part D spending across roughly 1.875 billion dosage units in 2023:
| Quantity | Value |
|---|---|
| Total spending | $18.3B |
| Total dosage units | ~1.875 billion |
| Spending per dosage unit | $9.74 |
So each Eliquis tablet cost the program about $9.74 on average. A 60-tablet monthly supply would be roughly $584 of program spending — close to its per-claim figure.
Per unit vs per claim vs per beneficiary
These three metrics answer different questions:
| Metric | Question it answers |
|---|---|
| Per dosage unit | How costly is the drug per pill/mL? |
| Per claim | How much does one prescription fill cost? |
| Per beneficiary | How much does the drug cost per patient per year? |
A high per-unit drug like Humira pen (over $3,750 per dosage unit) looks very different on a per-claim basis than a cheap generic taken daily.
What it is not
Spending per dosage unit is gross program spending, not net of confidential rebates, and not the price you pay. It is a comparison tool, not a price tag. This is general information, not medical or pricing advice.
Source: CMS Medicare Part D Spending by Drug, data year 2023, U.S. public domain.