Journal club: STEP 4 and what a withdrawal design can prove — one year on

Journal club: STEP 4 and what a withdrawal design can prove — one year on Writing it up because I had to work it out twice and would rather nobody else did.

Session topic: SURMOUNT-OSA (N Engl J Med, 2024). Please read it before posting; the discussion is much better when everyone has.

The question I would like us to start with is what the trial set out to estimate, rather than what it found. Once that is on the table we can talk about whether the design could have answered it, and only then about the numbers.

Specific things I would like covered: the population and how far it generalises, how discontinuation was handled, whether the comparator was a fair one, and what the absolute rather than relative effect looks like.

I will summarise at the end and the summary will feed the relevant digest page.

the opening post is right about the mechanism and I think understates the practical bit.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

Critical appraisal template: (1) What did the trial set out to estimate? (2) Could the design answer that question? (3) Was the population sufficiently similar to your population to apply the results? (4) What was the absolute effect, not just the relative one? (5) What are the two strongest criticisms available?

Session format: read the paper before posting. The discussion is much better when everyone has. Start with the estimand and population, then methods, then results, then limitations. That order makes critique coherent.

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

SURMOUNT-OSA (N Engl J Med 2024): Tirzepatide in obstructive sleep apnoea, using an objective physiological endpoint. Notable because soft endpoints are avoided. Two parallel trials addressed the confounder directly.

Coming back to post #5, because the follow-up matters more than the original answer.

FLOW (N Engl J Med 2024): Semaglutide renal outcomes in type 2 diabetes and chronic kidney disease. Stopped early for efficacy. Component-by-component analysis is essential because the components differ in how patient-important they are.

SURMOUNT-1 (N Engl J Med 2022): Tirzepatide obesity trial. The largest mean weight reduction for a pharmacological intervention at publication. Read the categorical thresholds carefully — they can exaggerate separation.

Worth separating two things that post #5 runs together.

SURPASS-2 (N Engl J Med 2021): Direct comparison of tirzepatide with semaglutide 1.0 mg. The 1.0 mg dose is not the highest available, which is the central and legitimate criticism of the head-to-head evidence.

SOUL (N Engl J Med 2025): Oral semaglutide cardiovascular outcomes. Extends the cardiovascular evidence to the oral formulation. Note that oral bioavailability is lower and more variable than injectable.

TRIUMPH (ongoing): Retatrutide phase 3. No results yet. Nothing should be attributed to it because it has not finished. When it does, this discussion will return to it.

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

Picking up post #10: that is the part I would want checked first.

PIONEER 6 (N Engl J Med 2019): Cardiovascular safety trial for oral semaglutide, not efficacy. Non-inferiority for safety was met. The trial was not designed to establish benefit, though point estimates favoured the drug.

Coming back to post #12, because the follow-up matters more than the original answer.

SELECT (N Engl J Med 2023): Semaglutide cardiovascular outcomes without diabetes. The first outcome trial in people without diabetes, which decoupled the cardiovascular argument from glucose control. Read the absolute numbers, not just the relative reduction.