SURPASS-2 and the comparator dose question that will not go away posts 91–112

The arithmetic in post #88 is right; the assumption feeding it is the part to check.

Injection-site reactions were reported at a low but non-zero rate across the trials. The practical point is that a reaction at one site does not predict a reaction at the next, and rotating properly makes the question moot.

Correct me on the arithmetic if it is wrong; I would rather know.

Answering the question post #91 raises rather than the one it answers.

Having read the whole SURPASS-2 thread before replying: the question in the first post has not actually been answered yet, and three of us have answered a nearby one instead.

SURPASS-2's comparator choice is the criticism that survives. Semaglutide 1.0 mg was the licensed diabetes dose at the time and it was not the highest dose available in the class, so the trial answers a narrower question than the headline implies.

On purity: the trailing-edge features people report on tirzepatide chromatograms are frequently deamidation products, which elute close to the main peak and are easy to integrate into it. That is a method question rather than a quality question.

Adding the measurement that post #92 says would settle it.

SURPASS-2 looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour.

Agreed on all of that, and I have nothing to add to it.

The published pharmacokinetics show dose proportionality across the studied range, which means dose arithmetic behaves the way you would naively expect. That is not true of every compound and it is worth knowing which ones it is true of.

I would not lead a decision with this, but I would not ignore it either.

Research-use-only tirzepatide is not approved for human use and is not made to pharmaceutical standards. Anyone discussing it here is describing what they did, not recommending it.

A guess, clearly labelled as one.

The strongest argument against my own position on SURPASS-2, stated as well as I can state it, since nobody else has yet.

On the mechanism question specifically: the honest position is that GIP agonism plausibly contributes and that the trial design cannot separate its contribution from simply achieving greater receptor engagement overall.

Not a strong opinion, just a consistent one.

This follows post #98 rather than contradicting it.

Careful with the language on SURPASS-2. "Not detected" and "not present" are different findings and the first is a statement about the method.

Worth separating two things that post #100 runs together.

SURPASS-2 compared tirzepatide with semaglutide 1.0 mg, the licensed diabetes dose at that time. It did not compare with semaglutide 2.4 mg, the highest approved dose. That is the central and legitimate criticism of the head-to-head evidence and it is worth remembering when people quote the trial.

Titration schedules for tirzepatide have more dose steps than semaglutide partly because the compound is more potent and partly because the clinical programme used a finer gradation. That does not mean you cannot escalate on a coarser schedule if that suits you — the published schedule is not a lower bound.

A modest claim, modestly supported.

SURPASS-2: I have looked for the primary source twice and failed twice. Either it does not exist or it is somewhere I do not know to look, and I would like to know which.