Peak-to-trough ratio at steady state for a weekly agent — the long version

Peak-to-trough ratio at steady state for a weekly agent — the long version Writing it up because I had to work it out twice and would rather nobody else did.

A narrow question about Peak-to-trough ratio, deliberately narrow, because the broad version has been asked here four times and produced four long threads and no answer.

One question, stated units, stated method, and what I have already ruled out.

Worth separating Peak-to-trough ratio as a question about the compound from Peak-to-trough ratio as a question about the documentation. They get answered by different people and only one of them is answerable here.

The arithmetic on Peak-to-trough ratio is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.

Peak-to-trough ratio came up in a thread eighteen months ago and was answered well. I cannot find it, which is itself the problem, so here is the reconstruction.

A missed weekly dose perturbs a slowly moving average rather than creating a trough. That is the pharmacokinetic reason the labelling does not recommend doubling.

The rule of thumb is fine; the edge cases are where it earns its keep.

I think the Peak-to-trough ratio question is answerable and has not been answered, which is a more optimistic position than most of this thread.

The most useful thing anyone has posted about Peak-to-trough ratio in this category was a table of what had been measured and by whom. That is what I would want again.

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

Building on post #54 rather than restating it.

Where two sources give different half-lives, check the study design before deciding either is wrong. Sampling duration, assay sensitivity and population all move the number.