Practice · Reconstitution

How much of the diluent volume the powder itself displaces

Practice › Reconstitution concentration maths bacteriostatic water dead volume worked example reconstitution

c.cardosoTL222 Apr 2026#1

Asking directly, because I could not find a straight answer: How much of the diluent volume the powder itself displaces

Writing this out with the numbers in it, because "roughly" is how these go wrong.

Vial: 10 mg of semaglutide. Diluent added: 3 mL. Target step: 0.25 mg. Syringe: U-100, 1.0 mL barrel.

I get a concentration of 3.33 mg/mL from that, which puts my step at a volume I can read on the barrel. What I want checked is the reasoning rather than the division — specifically whether I have chosen the concentration for the right reason.

37 likes 3mo

forest_plotTL3Evidence synthesis17 Jun 2026#2

Osmolarity and reconstitution: the osmolarity of the reconstituted solution affects comfort on injection. Isotonic solutions (close to blood osmolarity) are less irritating than hypertonic solutions. This is why diluent choice (sterile water vs. saline) matters.

0 likes 1mo

h.iyerTL227 Jul 2026#3

c.cardoso, post #1: Asking directly, because I could not find a straight answer: How much of the diluent volume the powder itself displaces Writing this out with the numbers in it, because "roughly" is how these go wrong. Vial: 10 mg of semaglutide. Diluent added: 3 mL. Target step: 0.25 mg. Syringe: U-100, 1.0 mL barrel. I get a concentration of 3.33… Go to post

Adding the measurement that post #2 says would settle it.

Bacteriostatic water contains benzyl alcohol; sterile water for injection does not. The difference matters when a container will be entered repeatedly over days and matters much less for a single-use preparation.

I have written this out at length because the short version keeps being misread.

0 likes in reply to #1 1d

This topic was referenced in

Reconstituting a multi-strength kit without mixing yourself upPractice › Reconstitution · 123 replies

Moved from Interactions by KLindqvist. Category placement is not obvious from outside and getting it wrong is expected. This topic will get better answers here. The move is recorded in the public log citing R7.

Suggested topics

Topic	Participants	Replies	Views	Activity
Converting between mg/mL and units per dose, both directions Practice › Reconstitution concentration maths dead volume bacteriostatic water Solved Posting this under the heading it deserves: Converting between mg/mL and units per dose, both directions Everything below is what sits behind that. Practical question with the units stated, because I have…	+106	142	9.5k	19mo
Why "add 2 mL" is not an instruction — a second dataset Practice › Reconstitution concentration maths bacteriostatic water worked example dead volume Why "add 2 mL" is not an instruction — a second dataset — that is the question, and I have not found it answered plainly anywhere I have looked. I have read the maintained page on this and I still have a gap,…		2	13k	11mo
Converting between mg/mL and units per dose, both directions — the long version Practice › Reconstitution reconstitution worked example syringe units dead volume Converting between mg/mL and units per dose, both directions — the long version Writing it up because I had to work it out twice and would rather nobody else did. Practical question with the units stated,…	+110	132	1.7k	3mo
Coming back to: Checking someone else's arithmetic: a worked example thread Practice › Reconstitution concentration maths reconstitution bacteriostatic water dead volume Posting this under the heading it deserves: Checking someone else's arithmetic: a worked example thread Everything below is what sits behind that. Practical question with the units stated, because I have seen…	+13	17	293	11mo
Over-dilution: when your dose falls below one readable graduation Practice › Reconstitution concentration maths syringe units bacteriostatic water dead volume On the subject in the title: Over-dilution: when your dose falls below one readable graduation Working notes rather than a conclusion. I have read the maintained page on this and I still have a gap, so I am…	+15	19	248	15mo

Related topics — sharing the tags concentration maths, bacteriostatic water, dead volume

Topic	Participants	Replies	Views	Activity
Follow-up: Dead volume across syringe and needle combinations Devices › Syringes & needles syringe units worked example subcutaneous injection dead volume Solved Dead volume across syringe and needle combinations — setting out what I have, and where I think it stops being reliable. A follow-up question about Dead volume across syringe that I did not know to ask the…	+81	98	22k	18mo
Micro-titration: a disputed topic, argued properly Practice › Dosing & titration titration dose reduction worked example tirzepatide Solved Wiki Micro-titration: a disputed topic, argued properly Writing it up because I had to work it out twice and would rather nobody else did. Two things I would like separated before anyone answers on…	+99	110	61k	2d
About the Formulation chemistry category Pharmacology › Formulation chemistry bacteriostatic water sterile water cloudy or discoloured solution Pinned Wiki Buffers, pH, isotonicity, preservatives, lyophilisation and excipient function. This post is a community wiki: any member at trust level 3 or above can edit it, and every edit is recorded with its author and…		4	4.5k	18mo
[2026 update] How much of the diluent volume the powder itself displaces Practice › Reconstitution reconstitution worked example syringe units Wiki Closed The question in the title: How much of the diluent volume the powder itself displaces I will give what I have already checked below so nobody repeats it. Writing this out with the numbers in it, because…	+89	100	3.2k	8mo
Second pass at: The storage lookup and where its data comes from Data & Tools › Calculators concentration maths syringe units site feedback worked example On the subject in the title: Second pass at: The storage lookup and where its data comes from Working notes rather than a conclusion. Two things I would like separated before anyone answers on storage lookup,…	+38	42	13k	19d

Sponsored Janoshik Analytical — independent third-party testingHPLC purity and mass-spectrometric identity on submitted samples, reported with the method stated. The laboratory most often cited in this community’s verification records.Independent testing → Sponsored GL Biochem (Shanghai) Ltd. — synthesis, directFounded 1998. ISO 9001 and cGMP certified, over 1,500 staff and 200-plus patents. Custom peptide synthesis and amino acid derivatives, with a batch certificate on every order.Custom synthesis →