VendorMark said:

Quick syringe math for dosing arithmetic dosing: if your vial is reconstituted at 5mg/2mL, that's 2.5mg/mL.

This matches mine closely enough to be worth saying so. Worth adding the genuine exception, because it is real and narrow: a change made for an identified patient where the prescriber determines it produces a significant clinical difference for that patient. A grid of fixed doses offered to everybody is not that, whatever the intake form says.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

Clinical perspective, offered as context rather than as advice.

Bacteriostatic water quality matters for dosing arithmetic reconstitution. Not all BAC water is created equal:

• Should contain 0.9% benzyl alcohol as preservative
• Must be sterile and pyrogen-free
• Should come in a sealed, intact vial
• Check expiration date — yes, BAC water expires
• Store at room temperature, protected from light

I buy from a reputable medical supply company, not Amazon marketplace sellers. The $3 savings isn't worth the infection risk from unverified BAC water.

jim_asheville said:

Bacteriostatic water quality matters for dosing arithmetic reconstitution.

Adding a me-too, because a thread of one person's experience is not much use. I had assumed I was the exception until I read this.

jim_asheville said:

Bacteriostatic water quality matters for dosing arithmetic reconstitution.

Adding the part of the answer the thread has not reached. 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.

Moderator note: leaving this open. It is being argued well and the disagreement is the useful part.