Usage Examples
- Purple Book shows the reference product's twelve-year exclusivity expired in March, so the 351(k) filing window is open.
- Three biosimilars are already licensed against that reference product per the Purple Book, and none of them is interchangeable.
- Pull the reference product's BLA number and first licensure date from the Purple Book before we lock the 351(k) cover letter.
What is Purple Book?
The Purple Book is FDA's searchable list of biological products licensed under the Public Health Service Act, recording each product's licensure date, reference-product exclusivity, and biosimilarity or interchangeability status.
The Purple Book exists because biosimilar development cannot start until two facts are settled: which product is the reference product, and when its exclusivity clocks expire. Congress required FDA to publish that information in a searchable electronic format, so sponsors, payers, and courts read the same list rather than reconstructing licensure dates from approval letters.
The Purple Book covers biological products licensed under the Public Health Service Act: CDER-regulated therapeutic biologics plus CBER-regulated vaccines, allergenics, blood products, and cellular and gene therapies, together with biosimilars and interchangeables licensed under section 351(k). It does not cover drugs approved under the Federal Food, Drug, and Cosmetic Act, and it is not an approval decision or a substitution mandate.
The Purple Book is applied at three points in a program. Sponsors read it during feasibility to fix the reference product and count four and twelve years forward from first licensure; regulatory operations carry the reference product's BLA number and licensure date into the 351(k) submission; and portfolio teams check whether an interchangeability determination already exists against that reference product.
Not to be confused with
- Orange Book
- the Orange Book lists drugs approved under the Federal Food, Drug, and Cosmetic Act and assigns therapeutic equivalence codes. The Purple Book lists products licensed under the PHS Act and carries biosimilarity and interchangeability evaluations instead; there are no TE codes in it.
- Biosimilar
- a biosimilar is a licensure pathway and a scientific finding about one product. The Purple Book is the public record that the finding was made. Listing follows licensure; it is not a status a sponsor applies for separately.
- Interchangeable biological product
- interchangeability is an additional statutory determination layered on top of biosimilarity, not a synonym for it. The Purple Book records which listings carry that determination, and most licensed biosimilars do not.
- BLA
- the BLA is the application a sponsor files and FDA reviews. The Purple Book is the downstream public list generated once that application is licensed, which is why the BLA number is the join key between the two.
The Purple Book itself imposes no obligations; the statute behind it does. These are the duties a 351(k) program is actually reading the list to satisfy.
What you must do
- 1Identify the reference product and its first licensure date before committing to a biosimilar program, because every exclusivity clock runs from that single date42 U.S.C. 262(k)(7)(A)
- 2Do not submit a 351(k) application until four years after the reference product was first licensed42 U.S.C. 262(k)(7)(B)
- 3Plan launch timing on the basis that approval cannot be made effective until twelve years after the reference product was first licensed42 U.S.C. 262(k)(7)(A)
- 4Support any interchangeability request with data showing the product can be expected to produce the same clinical result as the reference product in any given patient42 U.S.C. 262(k)(4)
- 5Re-verify listings against the live searchable database at each submission milestone rather than against a stored export, since FDA maintains the list publicly and updates it as licensure and exclusivity information changes42 U.S.C. 262(k)(9)
Common mistakes
Counting exclusivity from the wrong date
teams anchor the clock to a supplement, a new indication, or a new presentation instead of the reference product's first licensure. Both the four-year submission bar and the twelve-year effective-approval bar run from first licensure, so the error either wastes years of runway or produces a filing that cannot be accepted.
Reading a biosimilar listing as interchangeable
biosimilarity and interchangeability are separate findings under separate statutory tests, and most listed biosimilars carry only the first. Building a commercial case on substitution rights that were never granted overstates the addressable revenue and is caught late, usually by payers.
Working from a stale export
the Purple Book is maintained as a live public database; licensure, exclusivity, and patent fields move. A dossier or landscape deck built on a download from last year can cite a superseded reference-product status, which is a credibility problem in front of a reviewer and an expensive one in front of a partner.
When This Matters
- Purple Book shows the reference product's twelve-year exclusivity expired in March, so the 351(k) filing window is open.
- Three biosimilars are already licensed against that reference product per the Purple Book, and none of them is interchangeable.
- Pull the reference product's BLA number and first licensure date from the Purple Book before we lock the 351(k) cover letter.
Frequently Asked Questions
Twelve years from the date the reference product was first licensed, and a 351(k) application cannot even be submitted until four years after that same date. Both clocks in 42 U.S.C. 262(k)(7) run from first licensure, not from later supplements, new indications, or new presentations of the product.
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Sources & References
- Purple Book Search - FDA Database of Licensed Biological Products
- About Purple Book - Database of Licensed Biological Products
- Purple Book: Lists of Licensed Biological Products with Reference Product Exclusivity and Biosimilarity or Interchangeability Evaluations
- Background Information: List of Licensed Biological Products with Reference Product Exclusivity and Biosimilarity or Interchangeability Evaluations
- 42 U.S.C. 262 - Regulation of biological products (PHS Act section 351)
