10 days past a due dose is 1.43 half-lives at the seven-day half-life this class runs on, which leaves about 37.1 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^(10÷7) = 0.3715. At 37.1 per cent you have not been off it in any meaningful sense. The interval stretched from 7 days to 17 and the trough went lower than usual; that is the whole of what happened. 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.
Answer first: it depends on the half-life and on how long ago the dose was due, and for a weekly agent the tolerance is much wider than people fear.
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.
To change your regular dosing day, move the next dose later rather than earlier, keeping at least three days between doses for a weekly agent. Moving earlier compresses the interval and raises exposure.
Set a recurring reminder attached to something you already do weekly.
5The four-half-lives rule is the part everyone skips and it explains most of the misery. – Dr_Yusuf_Adeyemi 8 months ago add a comment