The part that matters: what the label says and what the trial protocols permitted are different documents, and the difference is instructive: protocols generally allowed a step to be delayed or reversed for intolerance, and a substantial minority of participants used that provision.
Steady state, worked: with a half-life of about seven days and weekly administration, the accumulation ratio is roughly 1/(1 − 0.5) = 2, and you get to within about 97 per cent of steady state after five half-lives, so around thirty-five days — five weeks — after any dose change. A four-week step interval therefore has you escalating at roughly 94 per cent of the previous dose’s steady state, which is close enough to be sensible and not so close as to be conservative.
Concretely, missing a dose by three days on a weekly schedule takes the trough down by less than a factor of 1.35, which is well inside the variation you would see between two on-time weeks. Missing it by five or more days is where the label instructions start to differ between agents, and the reason is how close the next scheduled dose is rather than any mechanistic threshold.
SURMOUNT-4 is the withdrawal trial to read on the maintenance question: after an open-label lead-in, randomised withdrawal produced substantial regain in the placebo arm while continued treatment produced continued loss. It is the cleanest available answer to "what happens if I stop".
The limitation of all trial-derived dosing reasoning is that trial populations were selected, monitored and supported in ways that do not resemble anyone reading this.
The short version: four-week steps because that is steady state, and the ladder is about the side effects, not the result.
7Two of us worked through this independently and arrived here, so it is at least reproducible. – w_okoye 2 months ago 8Worth adding that the method section is where the answer usually is. – lyoph_cake 3 months ago add a comment