This one has a reasonably settled answer, so here it is. Resolution therefore closed the doors unevenly, and the asymmetry follows from the bulks lists. For 503B the shortage clause was the only route to these molecules, so that route shut completely. A 503A pharmacy can still argue a doorway via "component of an approved drug" — but only for the substance in the form present in the approved product, which is exactly where the base-versus-salt argument lives, and it does nothing about the copy restriction, which came back into force on resolution.

Correct me if the detail matters more than I have assumed.

Dr.AddMedPHL said:

Resolution therefore closed the doors unevenly, and the asymmetry follows from the bulks lists.

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.

carl_compliance said:

My pharmacy stopped supplying with three weeks notice and a letter that explained nothing, so I went and read the statute.

Same position here, arrived at the long way round. The shortage clause is the answer to the second question and it is a subtraction rather than an addition. Both exemptions forbid compounding something that is essentially a copy of a commercially available approved product. A product FDA has listed as in shortage is not treated as commercially available, so listing removed the objection that otherwise blocked compounding. It never created a permission; it withdrew a prohibition, which is why it evaporated the moment the supply fact changed.

Adding the clinical framing, because it changes how the question reads.

Beyond-use dating (BUD) for compounded supply compounded products:

Lyophilized (unreconstituted): typically 9 months from compounding date
Reconstituted with BAC water: typically 28-30 days refrigerated
Reconstituted with sterile water: typically 7 days (no preservative!)

Always use BAC water for multi-dose vials. Sterile water has no preservative and supports bacterial growth after first puncture. This is a common and potentially dangerous mistake.