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Subcutaneous absorption kinetics and site differences

Pharmacology › Pharmacokinetics missed dose worked example semaglutide

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NicolaidesTL3Regular28 Apr 2025#1

Community wiki post. Any member at trust level 3 or above can edit this post; every edit is recorded. Last edited by trough_index on 31 Oct 2025.

12 May 2025 — g.pemberton_uk: Removed a claim that the cited source did not support.
5 Jul 2025 — ms_holloway: Replaced an unsourced figure with the published one and cited it.
31 Oct 2025 — trough_index: Added the worked example and a unit label to the table header.

Editors: g.pemberton_uk, ms_holloway, trough_index

Posting this under the heading it deserves: Subcutaneous absorption kinetics and site differences Everything below is what sits behind that.

Asking about subcutaneous absorption kinetics and site directly, because I have read four threads on it and each answered a slightly different question.

The version I want answered is the narrow one: given the method stated below, is the result within what anyone else has seen? I am not asking what it means yet.

Method, numbers and the two assumptions I am aware of making are below. If the assumptions are wrong that is more useful to me than agreement.

0 likes 15mo

r.vukovicTL28 May 2025#2

I had written a reply contradicting the opening post and deleted it. Here is what survived.

I would call the community position on subcutaneous absorption kinetics and site likely rather than established, and I would be comfortable defending that hedge.

2 likes 15mo

r.mcalisterTL3Regular15 May 2025 · edited#3

Thank you for the correction. I would rather find out here than later.

12 likes 14mo

r.nakamuraTL221 May 2025#4

Area under the curve is the exposure measure that matters for most effects in this class. Peak concentration matters more for tolerability.

The strength of my opinion here exceeds the strength of my evidence.

26 likes 14mo

system_suitabilityTL3Analytical chemist27 May 2025#5

Post #4 is the version of this I will quote in future. One addition.

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.

If this contradicts something upthread, the upthread version may well be the better one.

0 likes 14mo

j.moreauTL21 Jun 2025#6

system_suitability, post #5: Post #4 is the version of this I will quote in future. One addition. 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. If… Go to post

Where I part company with post #2, and it is a narrow parting.

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.

The literature is thinner on this than the confidence in the thread implies.

4 likes in reply to #5 14mo

k.otieno_statsTL3Statistician7 Jun 2025#7

Subcutaneous absorption kinetics and site: I have looked for the primary source twice and failed twice. Either it does not exist or it is somewhere I do not know to look, and I would like to know which.

18 likes 14mo

s.balogunTL212 Jun 2025#8

Bioavailability for subcutaneous administration in this class is high but not complete, and the published figures are formulation-specific.

0 likes 14mo

t.vasquezTL4 Moderator17 Jun 2025#9

Nicolaides, post #1: Posting this under the heading it deserves: Subcutaneous absorption kinetics and site differences Everything below is what sits behind that. Asking about subcutaneous absorption kinetics and site directly, because I have read four threads on it and each answered a slightly different question. The version I want answered is the narrow… Go to post

Building on post #8 rather than restating it.

The time to maximum concentration after a subcutaneous dose in this class is measured in days rather than hours, which surprises people expecting an injection to act quickly.

It took me longer than it should have to see that.

1 like in reply to #1 13mo

j.asanteTL221 Jun 2025#10

The practical upshot of week-long kinetics is that nothing you do this week is fully visible until next month. Most impatience in this field is a kinetics misunderstanding.

7 likes 13mo

MJayawardenaTL3Regular26 Jun 2025#11

I read post #9 twice before replying, because I had assumed the opposite.

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.

Posting it because the silence on this was starting to look like agreement.

6 likes 13mo

n.zielinskiTL21 Jul 2025#12

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.

Second-hand, so weight it accordingly.

1 like 13mo

DOdendaalTL3Regular5 Jul 2025#13

I have been on both sides of the subcutaneous absorption kinetics and site argument in this category within eighteen months, which should tell you how strong the evidence for either side is.

0 likes 13mo

b.teixeiraTL210 Jul 2025#14

j.moreau, post #6: Where I part company with post #2, and it is a narrow parting. 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. The literature is thinner on this than the confidence in the thread implies. Go to post

Taking post #13 at face value and following it one step further.

One caution on subcutaneous absorption kinetics and site: everything above assumes the underlying documentation is what it claims to be. That assumption is doing real work and is rarely stated.

23 likes in reply to #6 13mo

e.dalgleishTL3Regular14 Jul 2025 · edited#15

Subcutaneous absorption is the rate-limiting step for most of these compounds, which is why the apparent half-life is absorption-limited rather than elimination-limited.

It is worth checking rather than assuming, which costs nothing.

11 likes 12mo

r.ilungaTL218 Jul 2025#16

Nothing to add on the substance. Thank you for taking the question at face value.

3 likes 12mo

s.grahameTL2Member22 Jul 2025#17

n.zielinski, post #12: 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. Second-hand, so weight it accordingly. Go to post

Worth separating two things that post #13 runs together.

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.

I have left out the parts I could not verify.

0 likes in reply to #12 12mo

e.roosTL227 Jul 2025#18

t.vasquez, post #9: Building on post #8 rather than restating it. The time to maximum concentration after a subcutaneous dose in this class is measured in days rather than hours, which surprises people expecting an injection to act quickly. It took me longer than it should have to see that. Go to post

This follows post #17 rather than contradicting it.

Reading this subcutaneous absorption kinetics and site thread as someone who came in with a fixed view: the third and seventh replies moved me and the confident ones did not.

31 likes in reply to #9 12mo

f.abrahamsenTL2Member31 Jul 2025#19

A definition problem is doing most of the work in this subcutaneous absorption kinetics and site discussion. Once the term is pinned down I suspect the disagreement mostly goes away and what is left is small.

16 likes 12mo

e.coelhoTL24 Aug 2025#20

Confirming post #17 from a second method, which matters more than confirming it from a second person.

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.

6 likes 12mo

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Subcutaneous absorption kinetics and site differences

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