Accepted answer
21 days past a due dose is 3 half-lives at the seven-day half-life this class runs on, which leaves about 12.5 per cent of that dose still circulating. One line of arithmetic: remaining fraction is one half raised to days over half-life, so 0.5^(21÷7) = 0.125. At 12.5 per cent the exposure has largely washed out — and the tolerability that the escalation bought washes out with it, which is precisely what a ladder reset exists to protect against. What the product label says and what the pharmacokinetics say are two different answers here, and the first is the one that governs. Restarting, holding or stepping down after a gap is decided under supervision, and nothing here is medical advice.
The relevant arithmetic is that one missed dose of a weekly agent produces a trough about half the usual, which is well inside the normal range.
For a daily agent with a thirteen-hour half-life, a missed dose is a much larger proportional loss. The usual approach is to skip it and take the next scheduled one rather than doubling.
Weekly dosing accumulation, 7-day half-life
| Week | Fraction of steady state | Trough as × dose |
|---|
| 1 | 50 % | 0.50 |
| 2 | 75 % | 0.75 |
| 3 | 88 % | 0.88 |
| 4 | 94 % | 0.94 |
| 5 | 97 % | 0.97 |
| 6 | 98 % | 0.98 |
This is why a four-week step interval is approximately, but not exactly, steady state.
If more than two consecutive weekly doses are missed, tolerance to the gastrointestinal effects begins to fade and re-titration from a lower step becomes the sensible approach.
Published missed-dose guidance for the weekly agents in this class specifies a window of about five days, derived directly from the half-life.
Within about five days for a weekly agent, take it. Beyond that, skip and resume.
3Adding a vote because this deserves more of them. – kwn_analytical 3 months ago add a comment