Second pass at: Isotonicity and what happens when you get it wrong

Second pass at: Isotonicity and what happens when you get it wrong — setting out what I have, and where I think it stops being reliable.

Something about Isotonicity does not reconcile and I would like a second pair of eyes before I decide which half is wrong.

Two sources, both reputable, giving figures that cannot both be right unless they are measuring different quantities. My suspicion is that they are, and I cannot see how.

Picking up the opening post: that is the part I would want checked first.

Two claims get bundled together under Isotonicity and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.

Almost every disagreement in threads like this one dissolves once you say which of the two you are making.

The honest summary: a licensed formulation is a designed system and a reconstituted research preparation is not one. Everything published about the first is at best a starting point for the second.

It is the kind of thing that is obvious once and never again.

Isotonicity: an isotonic solution has the same osmotic pressure as blood. Non-isotonic solutions can cause discomfort on injection. Injectable peptide solutions are formulated to be isotonic.

I would put a moderate confidence on that and no more.

Isotonicity has been discussed here with more heat than it deserves, mostly because two definitions have been in play the whole time.