Pharmacology · Pharmacokinetics · continued

Washout: how long is long enough, and for what purpose posts 61–71

Pharmacology › Pharmacokinetics semaglutide missed dose worked example Closed

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.

compounding_ruthTL4Pharmacist30 Aug 2025#61

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.

0 likes 11mo

n.laurentTL22 Sep 2025 · edited#62

The documentation on washout is better than this thread and I say that as someone who has posted in the thread.

31 likes 11mo

t.vasquezTL4 Moderator5 Sep 2025#63

This is the first time the answer has come with its own limits attached. Appreciated.

10 likes 11mo

va.baptistaTL28 Sep 2025#64

so.cardoso, post #25: A pharmacokinetic model fitted to trial data describes the population studied. Applying it to somebody outside the enrolled range is an extrapolation, and the model will not tell you it is. Worth saying I have only my own numbers here, and n is small. Go to post

Taking post #62 at face value and following it one step further.

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.

3 likes in reply to #25 11mo

so.cardosoTL211 Sep 2025#65

Coming back to post #64, because the follow-up matters more than the original answer.

Metabolism for peptide drugs is proteolytic rather than hepatic in the usual sense, which is why the cytochrome interaction questions that dominate small-molecule pharmacology mostly do not apply.

0 likes 11mo

s.dziedzicTL213 Sep 2025#66

The bit of washout that nobody enjoys is that the answer changes depending on what you are trying to decide with it. Say what the decision is and the thread will converge.

23 likes 10mo

b.nilsenTL216 Sep 2025#67

I have three months of notes on washout and the honest summary is that the trend is real and the week-to-week numbers are noise. I nearly drew the opposite conclusion from the first fortnight.

6 likes 10mo

n.petrovTL219 Sep 2025#68

t.abubakar, post #20: Offering a way to settle washout rather than another opinion about it. Two measurements, taken the same way, a fortnight apart. If the difference is within the noise, the question was not answerable at this precision. Go to post

This follows post #67 rather than contradicting 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.

If anyone has run this properly I would rather read that than my own guess.

1 like in reply to #20 10mo

endpoint_marginTL222 Sep 2025#69

Collapsed as off-topic by two members at trust level 3 or above

Something worth flagging about washout: the strongest-sounding claims in this thread are the ones with no source attached, which is the usual pattern and not a coincidence.

s.vogelTL225 Sep 2025#70

Confirming post #67 from a second method, which matters more than confirming it from a second person.

Where the washout discussion usually stalls is that nobody wants to say "I do not know" and everyone is willing to say "it varies". Those are the same sentence with different clothes on.

0 likes 10mo

z.yildizTL227 Sep 2025#71

z.onwuka, post #14: Checked the washout claim against the primary source this morning. It survives, with a narrower scope than the version quoted here. Posting the narrower scope. Go to post

1 like in reply to #14 10mo

This topic was referenced in

Half-life, steady state, and accumulation worked throughPharmacology › Pharmacokinetics · 130 replies

This topic was closed 45 days after the last reply. Closing is automatic for quiet topics so that a settled answer does not collect new questions underneath it. If you have a follow-up, open a new topic and link back to this one — that keeps both readable and gives your question its own title.

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