BenResearch_OR said:

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

Pushing back on BenResearch_OR here. A research-chemical supplier selling lyophilised powder labelled research use only is not compounding and is not claiming to. It is a different legal universe with no pharmacy oversight, no patient relationship and no content guarantee, and conflating the two in these threads helps nobody.

The figures, for anyone assembling their own picture. For anyone assembling their own picture: Tmax is one to three days, terminal half-life about 165 to 170 hours, steady state at four to five weeks, and subcutaneous bioavailability near 89%. Those four numbers explain most of the questions people ask about timing.

BethLabQueen said:

A research-chemical supplier selling lyophilised powder labelled research use only is not compounding and is not claiming to.

There is a second half to this that has not been said yet. Steady state is the thing most people miss. The terminal half-life is about a week, so every dose step takes four to five weeks to fully express itself. Judging a step at day ten is judging the ascent, not the plateau, and it is the single commonest reason people escalate before they needed to.

Following on from PurityPaulOR — and this may be the naive question:

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

Reporting back.

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.