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What did the placebo arm of SURMOUNT-2 report for reflux?

Asked 28 Jun 2024Modified 22 months agoViewed 25k times
31

Stated plainly: SURMOUNT-2 · reflux.

I have read the primary source rather than the summary, which has left me with more questions.

I understand the headline. I do not understand the footnotes, and the footnotes look important.

What would I need in addition before this supported a decision?

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askedarea_percent9.9k1628 Jun 2024

5 Answers

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63

The SURMOUNT-2 placebo arm is the only thing that makes its treatment arm interpretable, and it is the row nobody quotes. Symptoms reported under placebo in these programmes are not rare, because the population is being asked about them weekly and would have had some of them regardless. The attributable figure is the treated rate minus the placebo rate, and that difference is routinely a fraction of the headline. Two cautions on the subtraction: the arms must have been assessed the same way, and a discontinuation for an event removes that participant from later time points in both arms, which flatters whichever arm loses more people.

The trial answers a narrower question than the headline suggests, and the narrowing is where the useful information is.

Placebo arms in this class are not nothing. Lifestyle-intervention placebo arms in the major obesity trials commonly lose two to three per cent of body weight, so an active-arm figure quoted without its comparator overstates the drug effect by roughly that much.

Duration decides what can be seen. A 68-week trial can measure weight and glycaemia; it cannot measure anything whose event rate is one per cent per year without enrolling tens of thousands.

If a claim cannot be traced to a named trial with a named endpoint, treat it as a claim rather than as evidence.

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DF
answeredDr_Nadia_Farsi104k24710 Jul 2024
5Absolute risk reduction rather than relative would make this much more useful. – Dr_Marek_Zielinski 8 months ago
6Which population was that figure from? It moves a lot between the trials. – kwn_analytical 9 months ago
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41

Before comparing two trials, check whether they share an endpoint definition. Frequently they do not, and the numbers then are not comparable in any sense.

A composite endpoint is only as informative as its least serious component. Where a cardiovascular composite combines death, infarction and stroke, ask which component moved, because they are not interchangeable outcomes.

Non-inferiority and superiority designs are not interchangeable. A non-inferiority result says the new agent is not meaningfully worse against a pre-specified margin — it does not say it is as good, and it certainly does not say it is better.

Registry entries at ClinicalTrials.gov carry the pre-specified primary endpoint with a timestamp, which is the cheapest available check on whether an endpoint was changed after the data were seen.

Quote the interval alongside the estimate and half the disagreements on this site would not start.

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KA
answeredkwn_analytical147k35821 Jul 2024
6Is the open-label extension included in that figure, or just the randomised phase? – Dr_Rosalind_Achebe 5 months ago
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34

The short version: the effect is real, the magnitude depends on the population, and the population is usually the part that gets dropped when a result is quoted second-hand.

Open-label extensions are not the same evidence as the randomised phase. Once everyone knows what they are taking, the reported outcomes acquire a bias that no analysis fully removes.

Trial populations are selected. Exclusion criteria in this class routinely remove people with significant renal impairment, prior pancreatitis and unstable psychiatric illness, which is exactly the population the results are then quoted for.

I am not a clinician and this is not medical advice; it is a reading of a published protocol.

When two sources disagree, the answer is almost always in the methods section of the one you have not read.

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HP
answeredh_pergande71k1581 Aug 2024
27

Concretely, a trial establishes what happened to a defined group under a defined protocol. Extending it beyond that group is inference, and inference is allowed as long as it is labelled.

Intention-to-treat and per-protocol analyses answer different questions. ITT asks what happens if you offer the treatment; per-protocol asks what happens if it is taken as directed. The gap between the two is a measure of how tolerable the protocol was.

Meta-analyses in this area are dominated by whichever trial contributed the most participants, so read the forest plot rather than the summary estimate.

Read the protocol and the statistical analysis plan if the result matters to you. Both are usually published alongside.

edited 15 Aug 2024 by Dr_Ilse_Vandenberg — added the placebo-arm figures

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DV
answeredDr_Ilse_Vandenberg113k24812 Aug 2024
24

The honest answer here is that the published evidence supports part of the claim and is silent on the rest, and it is worth being precise about which part is which.

Confidence intervals matter more than point estimates when two trials disagree. Two studies reporting fifteen and twenty per cent whose intervals overlap heavily have not disagreed about anything.

One qualification: absence of a signal in a trial of this size is not evidence of absence for a rare event. It is evidence that the event is rarer than the trial could detect.

The short version: check the endpoint, check the comparator, check who was excluded, then look at the number.

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CR
answeredcoring_risk27k2724 Sept 2024
2Worth flagging that this changed with the 2025 publication, so older answers are out of date. – lipid_panel_q 3 months ago
3Adding a vote because this deserves more of them. – h_pergande 4 months ago
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Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.

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