Coming back to: Washout: how long is long enough, and for what purpose posts 91–120

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

Individual variation: people vary in how quickly they absorb, distribute, metabolise, and excrete these compounds. That variation is partly genetic and partly due to individual biology (gut motility, kidney and liver function). It explains why two people on the same dose have different response magnitudes.

Coming back to post #105, because the follow-up matters more than the original answer.

Volume of distribution: the theoretical volume the drug distributes into. For albumin-binding compounds, volume is reduced compared to drugs that do not bind protein. That is relevant to understanding how much free drug is available.

Half-life: semaglutide ≈ 165–184 hours (about a week). Tirzepatide ≈ 5 days. Liraglutide ≈ 13 hours. The half-life determines how much accumulation happens at steady state and how long it takes to clear after stopping.

Worth separating two things that post #105 runs together.

Fasting requirement for oral semaglutide: food and large fluid volumes reduce absorption. The fasting window (30 minutes before and 30 minutes after) is designed to maximise absorption. Violating it measurably reduces exposure.

Accumulation at steady state: with a week-long half-life, steady-state concentration is reached around 4 to 5 half-lives (about 4 to 5 weeks). Before that, concentration is rising with each dose. The clinical implication: escalating before 4 weeks means escalating before steady state.

This follows post #108 rather than contradicting it.

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

Albumin binding: semaglutide binds albumin through a fatty side chain, which sequesters the free form and extends the half-life. Tirzepatide also has albumin binding (different mechanism) which extends its half-life compared to an unmodified peptide.

Hepatic metabolism: the degree to which each compound is hepatically metabolised versus renally cleared is known but varies. Severe liver disease changes clearance.

Worth separating two things that post #110 runs together.

Volume of distribution: the theoretical volume the drug distributes into. For albumin-binding compounds, volume is reduced compared to drugs that do not bind protein. That is relevant to understanding how much free drug is available.

Picking up post #112: that is the part I would want checked first.

Individual variation: people vary in how quickly they absorb, distribute, metabolise, and excrete these compounds. That variation is partly genetic and partly due to individual biology (gut motility, kidney and liver function). It explains why two people on the same dose have different response magnitudes.

Coming back to post #114, because the follow-up matters more than the original answer.

Half-life: semaglutide ≈ 165–184 hours (about a week). Tirzepatide ≈ 5 days. Liraglutide ≈ 13 hours. The half-life determines how much accumulation happens at steady state and how long it takes to clear after stopping.

Accumulation at steady state: with a week-long half-life, steady-state concentration is reached around 4 to 5 half-lives (about 4 to 5 weeks). Before that, concentration is rising with each dose. The clinical implication: escalating before 4 weeks means escalating before steady state.

Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.

The correction was fair and I had been repeating something I had not checked carefully enough.

Bioavailability: oral semaglutide has low bioavailability (roughly 1%) due to peptide instability. That is why the oral dose (14 mg) is so much larger than the injectable dose. Comparing them by mass is meaningless.

I read post #118 twice before replying, because I had assumed the opposite.

SNAC (the oral bioavailability enhancer): sodium N-(8-[2-hydroxybenzoyl]amino) caprylate transiently raises gastric pH and promotes absorption. Without it, oral bioavailability is too low for clinical use. With it, bioavailability is still variable between people.