503A vs. 503B Facilities: What Your Veterinary Practice Needs to Know

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Veterinary hospitals have always been challenged to find right-fit medications for their patients, repurposing and compounding human drugs for companion animals. Pharmaceutical compounding is a valuable and often misunderstood practice, steeped in history and tradition. Modern compounding—often referred to as 503A—provides patient-specific formulations to meet individual patient needs. Because commercially available drugs are marketed almost exclusively for humans, compounding has become an essential resource, allowing for preparations at lower concentrations and more palatable dosage forms to optimize treatment for their patients.

However, without proper oversight, the potency and consistency of these drugs may vary, which creates a risky situation for patients and increased liabilities for veterinary practices. With the introduction of 503B manufactured veterinary medications, these expanding product options gives peace of mind for clients and prescribers, more consistency, and better patient outcomes.

What’s the Difference Between 503A and 503B?



Type of Facility

Traditional compounding pharmacy

Outsourcing facility that manufactures drugs

Main regulatory oversight

State Board of Pharmacy



USP <795>, <797>, <800>, SBOP

FDA 21 CFR Part 210 and 211 (cGMP)

FDA inspections

For cause (approx. 3k compounding pharmacies)

Random inspections (approx. 69 facilities)

Engineering control smoke studies to assess proper air flow

Per area

Per area & each process

Stability testing of formulation to assign expiration date

Sterility testing as release test for finished product testing (USP General Chapter <71>)

Limited – Only with extended dating and high-risk batches

Finished product testing (potency, endotoxins)

Continuous non-viable particle monitoring during aseptic processing

Viable monitoring to determine microbial control

Air-twice yearly, surface-routinely, personnel-initially & 1-2/yr

Daily (air, surface, personnel) and every batch

Personnel gown monitoring

Twice yearly

Per batch

Personnel gloves monitoring

Once daily

Per batch

Retain sampling

High level of documentation to ensure process traceability & tracking

Process & equipment validations

Independent quality department (separate from production)

Increased Testing: cGMP vs. USP

Traditional compounding pharmacies must operate under standards put forth by the United States Pharmacopoeia (USP), specifically USP Chapter <795> (non-sterile compounding) and USP Chapter <797> (sterile compounding), but there are many differences between USP and cGMP, or current Good Manufacturing Processes. The most fundamental difference is the amount of testing required, including:

  • Potency testing of every batch to make sure the product meets label claims
  • Sterility testing if the product claims sterility
  • Endotoxin testing for injections

These tests are either not required or only conditionally required in a 503A pharmacy.

Batch-to-Batch Consistency

Many traditional compounding pharmacies go beyond minimum requirements for 503A processing, but even those that advertise potency testing, for instance, there is no guarantee that it was done for the specific batch given to a patient.

Recently our staff was working with a veterinary ophthalmologist whose glaucoma medication was not achieving the desired effect on her patients. Some units she used worked as expected and others did not. The medication was ordered from a large-volume traditional 503A compounding pharmacy. After some testing, it was determined that the variability was due to fluctuations in potency from lot-to-lot. When replaced with the same product from Epicur with potency testing to ensure effectiveness, the veterinarian had no further issues.

Improved Patient Outcomes

Veterinarians must often find a balance when it comes to prescribing. Price, convenience, and availability can mean improved compliance. Some clients may benefit from a specifically formulated dosage that falls outside of the standard dosages available from a 503B facility. Other situations call for the manufactured standard dose, which undergoes strict testing for guaranteed accuracy and strength throughout the product’s life. With expanding options, veterinarians can make the right choice for their client and patient, assured that their order meets standards of safety and quality, if they know what to look for in a compounding facility.


Interested in learning more about the difference between 503A and 503B? Our informational video breaks down the two types of facilities:

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The Best of Both Worlds

As sister companies, Epicur Pharma and Stokes Pharmacy can partner with you to ensure you get the right medicines at the right time for your patients:

  • Stokes fills individual prescriptions with a variety of shipping options
  • Epicur manufactures your in-office bulk medications for the convenience and revenue potential of dispensing in-house.

Epicur Pharma™ is a pioneering 503B facility manufacturing the highest quality and largest selection of traditionally compounded drugs for veterinary practices. Our commitment to drug consistency and quality emphasizes our devotion to patient safety.

Check out our product portfolio and learn how Epicur’s reliability reduces practice liability, improves patient outcomes, and allows veterinarians to trust in the medications they use and prescribe.

For a deeper dive on the key differences between 503A and 503B facilities, download our white paper.

The Importance of cGMP (503B) Compounded Drugs: 

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