Splitting a weekly dose in two: the pharmacokinetic argument against

Splitting a weekly dose in two: the pharmacokinetic argument against — setting out what I have, and where I think it stops being reliable.

I have read the maintained page on this and I still have a gap, so I am asking rather than guessing.

Context: semaglutide, 4 weeks in, currently at a dose I reached by the standard four-week steps. Everything below is my own record rather than anything a clinician told me.

The specific question is the one in the title. What I have already checked: the labelling summary on the relevant documentation page, the two most-linked topics in this subcategory, and my own notes from the last 9 weeks. What I could not find is whether the answer changes at higher doses or whether it is the same arithmetic throughout.

If the answer is "it depends", I would rather know what it depends on than be given a number.

Building on the opening post rather than restating it.

A missed dose in a weekly schedule is not a trough to chase. With a week-long half-life you are perturbing a slowly moving average, and the labelling for licensed products in this class says take it if the next dose is far enough away and skip it otherwise.

Escalating before steady state means you are judging a dose you have not yet fully experienced. That is the whole argument against compressing the schedule and it is a good one.

It is one reading of the data and not the only reasonable one.

Holding at a dose that is working is a legitimate position and it is not what the trial protocols did. The protocols escalated to a target because they were measuring the target dose, not finding each person's minimum.

That is a description of practice, not a recommendation of it.

This settles it for me, at least until somebody posts a reason it should not.

Post #3 is the version of this I will quote in future. One addition.

How the published trials escalated: they used specific step sizes and intervals. The STEP programme used a particular cadence; the SURPASS and SURMOUNT programmes used slightly different ones. Reading them side by side shows the variation is real but small.

Post #3 describes the usual case. This is about the unusual one.

Splitting a weekly dose in two: the pharmacokinetic argument against is that you want the benefit of long half-life, which gives a slowly changing plasma level from a weekly dosing schedule. Splitting it flattens the curve further but loses the convenience of once-weekly dosing. The trade-off is convenience versus a slightly flatter concentration curve.

Titrating on tolerability rather than on the calendar: some people escalate when they tolerate a dose well, others escalate on the prescribed schedule regardless. The published trials used a calendar-based schedule. Tolerability-based escalation has no formal evidence base but is not uncommon in practice.

The interesting part of this is the exception, and I do not understand the exception.

If you are stepping up mainly because the schedule says so rather than because the current dose has stopped doing what you wanted, that is worth noticing before rather than afterwards.

It is worth stating the boring hypothesis before the interesting one.

The four-week escalation interval is a convention from the pivotal trials, not a pharmacological constant. The pharmacological argument is that with a week-long half-life, four weeks approaches steady state and you can assess the dose fairly. That is an argument for not going faster. It is not an argument against going slower.

Somebody will have a better source than mine, and I hope they post it.

Post #8 answers the question as asked. The question underneath it is different.

Speaking only to splitting a weekly dose as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.

I read post #10 twice before replying, because I had assumed the opposite.

A request rather than an answer: could whoever has the primary source for splitting a weekly dose post it? I have seen the claim three times this month and each version had lost a qualifier.

Reaching a dose and staying there for a year: the question of whether a stable dose remains effective over years is mostly answered by the withdrawal trials and by real-world reports. The dose does not seem to stop working, but the longest trials are not indefinitely long.

When a dose reduction is the correct response to a side effect: if a side effect is dose-dependent (nausea, constipation, injection discomfort), reducing the dose is a reasonable response. If the side effect is not dose-dependent (e.g., hypoglycemia with insulin), dose reduction does not address the issue.

The disagreement above is smaller than it looks once the terms are fixed.