A Glossary of FDA Compounding Terms: 503A, 503B, NPRM, Bulks List, DFO
October 5, 2026
Why a glossary helps
Compounding coverage mixes statutory sections, advisory bodies, and rulemaking jargon. This glossary is educational — not legal advice — and focuses on terms that appear repeatedly in 503A bulks discussions.
### 503A
Section of the FD&C Act governing traditional pharmacy compounding pursuant to an individual prescription under specified conditions. Bulk substances used under 503A generally must meet listing and other statutory requirements.
### 503B
Section governing outsourcing facilities — a different compounding pathway with its own registration, reporting, and quality expectations. Do not assume a 503A concept applies unchanged to 503B (or the reverse).
### Bulks List / Category 1
The affirmative list of bulk drug substances that may be used in 503A compounding when other conditions are met, developed through FDA rulemaking.
### Category 2
The posture associated with substances FDA has identified as presenting significant safety risks for compounding. Distinct from Category 1 listing.
### PCAC
Pharmacy Compounding Advisory Committee — FDA advisory committee that may recommend for or against adding nominated bulk substances to the 503A list.
### DFO
Designated Federal Officer — the FDA official who administers the federal advisory committee meeting process.
### NPRM
Notice of Proposed Rulemaking — the Federal Register publication that proposes regulatory text and opens public comment before a final rule.
### Final rule
The completed regulation published after notice and comment. For 503A bulks additions, this is the ordinary endpoint of formal listing.
### Nomination
A stakeholder submission asking FDA to evaluate a bulk drug substance for potential listing. Nomination starts review; it does not grant listing.
### Non-binding recommendation
Advisory committee advice that informs FDA but does not itself change the Code of Federal Regulations or approve a drug.
How to use this glossary when reading news
Map every headline claim to one term above. If an article says “approved” but describes a PCAC vote, the glossary term you want is **non-binding recommendation**, not drug approval.
*For research use only. Not for human or animal consumption.*
USX Peptides Team
Our research and quality team at USX Peptides.