Tirzepatide in obstructive sleep apnoea: reading SURMOUNT-OSA

Posting this under the heading it deserves: Tirzepatide in obstructive sleep apnoea: reading SURMOUNT-OSA Everything below is what sits behind that.

Reading back through what has been written here about tirzepatide in obstructive sleep apnoea, three questions come up every time and only one has ever been answered properly.

Listing all three, with what I think the state of the answer is for each, so the thread can start further along than the last one did.

The opening post describes the usual case. This is about the unusual one.

Comparisons between the tirzepatide and semaglutide programmes across trials rather than within one are weak. Different populations, different durations, different baseline characteristics; the only fair comparison is a head-to-head one.

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.

It cost nothing to check and would have cost something not to.

SURMOUNT-OSA is notable because it used an objective physiological endpoint, the apnoea-hypopnoea index, rather than a symptom scale. Two parallel trials, with and without positive airway pressure, addressed the confounder directly. The reduction was substantial in both.

This is the sort of thing that ought to be settled and apparently is not.

The arithmetic in post #4 is right; the assumption feeding it is the part to check.

The GIP component: GIP receptor agonism is thought to amplify the GLP-1 effect on satiety and energy expenditure, but how much of tirzepatide's effect is that and how much is simply achieving higher receptor occupancy remains genuinely open. The mechanistic literature is active.

Mass and charge states: tirzepatide is about 4813.5 Da and on an electrospray instrument you would expect to see charge states mostly in the 2+ to 4+ range, the same as semaglutide. A doubly charged species would appear at about (4813.5 + 2 × 1.008) / 2 ≈ 2408.

The short version is the first sentence; the rest is why.

Dual agonism versus dose: how much of tirzepatide's effect is the GIP component and how much is simply achieving higher receptor engagement? The honest answer is that the question is not settled. Some of the effect is surely the GIP component, but the trial design does not decompose it.

I would want to see it done twice before believing it once.

Helpful, and short, which on this subject is harder than long.