Topic summary

[2026 update] How much of the diluent volume the powder itself displaces

Practice › Reconstitution reconstitution worked example syringe units Wiki Closed

This is a generated summary. It shows the 9 most-liked posts from a topic of 101, in their original order, with the accepted answer included where one exists. It is a reading aid and it will miss nuance — the full topic is the record.

f.weissTL222 Nov 2025#2

Community wiki post. Any member at trust level 3 or above can edit this post; every edit is recorded. Last edited by a.reyes on 10 Jun 2026.

13 Dec 2025 — policy_reader: Clarified the distinction that was causing repeat questions below.
19 May 2026 — a.thorne: Added the worked example and a unit label to the table header.
17 Jun 2026 — a.salcedo: Replaced an unsourced figure with the published one and cited it.
10 Jun 2026 — a.reyes: Removed a claim that the cited source did not support.

Editors: policy_reader, a.thorne, a.salcedo, a.reyes

The opening post is the version of this I will quote in future. One addition.

Preservative effectiveness is tested against a defined microbial challenge under defined conditions. It is not a licence to treat an entered vial as sterile indefinitely, and no supplier claims otherwise.

That is a description of practice, not a recommendation of it.

27 likes 8mo

r.danquahTL223 Nov 2025#17

A 10 mg vial reconstituted three different ways: 1 mL diluent gives 10 mg/mL, 2 mL gives 5 mg/mL, 4 mL gives roughly 2.5 mg/mL. The arithmetic is the same; the concentration determines which syringe graduations are legible.

29 likes 8mo

a.kravchenkoTL223 Nov 2025#23

I read post #19 twice before replying, because I had assumed the opposite.

How much of the diluent volume the powder itself displaces: for a small peptide vial, the powder volume is negligible. For a larger vial or a kit with multiple compounds, the displacement can be a few tenths of a millilitre. If precision matters to you, account for it by targeting a final weight rather than a final volume.

31 likes 8mo

n.villalobosTL224 Nov 2025#31

Adding the measurement that post #29 says would settle it.

Anyone who has looked at this more carefully, please correct the record.

32 likes 8mo

e.adeyemiTL225 Nov 2025#57

If your arithmetic gives a volume smaller than one graduation on your syringe, the answer is a lower concentration rather than a more careful hand.

28 likes 8mo

s.ostergaardTL225 Nov 2025#65

Birkeland, post #24: Post #23 answers the question as asked. The question underneath it is different. Add the diluent down the side of the vial rather than directly onto the cake. It is slower and it avoids the foaming that makes people think something has gone wrong. Go to post

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

32 likes in reply to #24 8mo

cannula_driftTL3Regular26 Nov 2025#75

The arithmetic in post #73 is right; the assumption feeding it is the part to check.

The lyophilised cake should be inspected before anything is added. A shrunken, collapsed or discoloured cake is information, and it is information you lose the moment you add diluent.

Filing this under things that are true until someone shows me otherwise.

26 likes 8mo

j.baptistaTL226 Nov 2025 · edited#85

If your arithmetic gives a volume smaller than one graduation on your syringe, the answer is a lower concentration rather than a more careful hand.

27 likes 8mo

r.novakTL226 Nov 2025#91

CSagredo, post #71: Adding thanks rather than a view. I do not have a view worth the space. Go to post

The lyophilised cake should be inspected before anything is added. A shrunken, collapsed or discoloured cake is information, and it is information you lose the moment you add diluent.

A partial answer, offered because a partial answer beats none.

29 likes in reply to #71 8mo

Read the full topic (101 posts)

This topic was referenced in

A vial that will not fully dissolve: what to check and in what orderPractice › Reconstitution · 16 replies
Swirling versus inverting versus leaving it alonePractice › Reconstitution · 2 replies
Reconstitution volumes that produce round numbers, tabulatedPractice › Reconstitution · 112 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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