LipidDoc_ATL said:

They are two different exemptions from the same federal requirements and they buy different things.

GMP compliance checklist relevant to compounded supply compounding quality:

• Clean room environment with HEPA filtration
• Environmental monitoring (viable and non-viable)
• Personnel training and competency assessment
• Validated analytical methods for testing
• Stability testing program
• Complete batch records and traceability
• Quality management system with deviation handling

A 503B pharmacy following cGMP should be able to answer questions about ALL of these if you ask. Don't be afraid to ask — it's your health.

One thing that is still open after claudia_zurich’s answer:

What actually distinguishes 503A from 503B, in terms of what each may make and from what starting material?

lisa_labSD said:

GMP compliance checklist relevant to compounded supply compounding quality: Clean room environment with HEPA filtration Environmental monitoring…

Compounding pharmacy customer here with experience relevant to compounded supply.

I've ordered from 3 different compounding pharmacies over the past year. The quality variation is real — purity ranged from 94% to 101% of label claim based on independent Janoshik testing.

My current compounder (a 503B facility) has been consistently 98-101% purity across 6 orders. I pay $110/month vs $1,320 for brand. The savings are substantial and the product is equivalent in my experience.

Re: compounded supply — this applies whether you're using brand or compounded. The clinical principles are the same.

Closing the loop on my own question.

The bulks-list asymmetry was the piece I had missed entirely. It explains why one of my two pharmacies is still arguing it can supply and the other simply stopped.

PharmacoVig_BOS said:

Compounding pharmacy customer here with experience relevant to compounded supply.

Agreed, and the enforcement dates were staggered by category — 503A first, 503B a few weeks later — because outsourcing facilities have manufactured inventory and clinic contracts to unwind while a 503A makes to order.