Dermatology practices rely on compounded topicals more than almost any other specialty: custom-strength retinoids, combination acne preparations, compounded minoxidil formulations, diluted corticosteroid bases. Where that product actually comes from, a 503A pharmacy or a 503B outsourcing facility, determines the regulatory standard it was made under, and it's worth knowing the difference cold.

503A: The Traditional Compounding Pharmacy

503A refers to the section of the Federal Food, Drug, and Cosmetic Act covering traditional pharmacy compounding. A 503A pharmacy compounds for an individual, identified patient, generally requires a patient-specific prescription, and is regulated primarily by the state board of pharmacy rather than the FDA. 503A compounding isn't subject to FDA current Good Manufacturing Practice (cGMP) requirements, but it is expected to follow USP compounding standards, most notably USP <795> for nonsterile preparations and USP <797> for sterile ones.

Critically, a 503A pharmacy generally cannot compound a preparation that's "essentially a copy" of a commercially available drug product, with one major exception: during an FDA-declared drug shortage, that restriction lifts for the duration of the shortage.

503B: The Outsourcing Facility

503B refers to "outsourcing facilities," a category created by the Drug Quality and Security Act of 2013. Unlike 503A pharmacies, 503B facilities register with the FDA, are subject to cGMP requirements, and are subject to routine FDA inspection, more like a small-scale manufacturer than a traditional pharmacy. 503B facilities can compound in larger batches without a patient-specific prescription, commonly called "office use," supplying hospitals, clinics, and physician practices directly.

503B facilities compounding from bulk drug substances (rather than an FDA-approved finished drug product) can only use substances on the FDA's 503B Bulks List, a list the FDA maintains and periodically revises based on clinical need determinations.

Why the Distinction Matters in Practice

  • Sourcing for office-use quantities (a dermatology practice stocking a compounded topical for multiple patients) generally requires 503B sourcing, since 503A compounding is tied to individual patient prescriptions.
  • Quality assurance expectations differ. A 503B product carries cGMP-level manufacturing controls and FDA inspection history; a 503A product's quality assurance rests on the individual pharmacy's USP compliance and state board oversight.
  • The shortage-copy exception is temporary by design. When an FDA-declared shortage resolves, 503A pharmacies must stop compounding copies of the now-available commercial product. See our companion piece on the intralesional triamcinolone shortage for how this plays out with a drug dermatology practices use every day.

The Practical Takeaway

Knowing whether a compounded product in front of you came from a 503A or 503B source isn't a technicality, it tells you what regulatory and quality framework that product was made under, and what questions are worth asking if something seems off.

This is an educational overview and does not constitute legal, regulatory, or pharmaceutical advice. Compounding decisions should always follow current FDA and USP standards, state board of pharmacy requirements, and your organization's policies.