Practice · Reconstitution

Why I now write the concentration on the vial in marker

Practice › Reconstitution syringe units bacteriostatic water concentration maths

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compounding_ruthTL4Pharmacist22 Jun 2026#1

Asking directly, because I could not find a straight answer: Why I now write the concentration on the vial in marker

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

Vial: 15 mg of tirzepatide. Diluent added: 3 mL. Target step: 0.25 mg. Syringe: U-100, 0.5 mL barrel.

I get a concentration of 5.00 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.

1 like 1mo

an.ibarraTL229 Jun 2026#2

Quietly grateful for the plain phrasing. Not every thread gets that.

4 likes 29d

TL4_HalvorsenTL4Leader · Journal club4 Jul 2026#3

compounding_ruth, post #1: Asking directly, because I could not find a straight answer: Why I now write the concentration on the vial in marker Writing this out with the numbers in it, because "roughly" is how these go wrong. Vial: 15 mg of tirzepatide. Diluent added: 3 mL. Target step: 0.25 mg. Syringe: U-100, 0.5 mL barrel. I get a concentration of 5.00 mg/mL… Go to post

Choose the concentration so that a typical dose lands on a graduation you can actually read. A dose that falls between two marks on a 1 mL barrel is a dose you will get wrong sooner or later.

Not a strong opinion, just a consistent one.

13 likes in reply to #1 24d

c.amankwahTL29 Jul 2026#4

Two people can reconstitute the same vial to different concentrations and both be right. The dose is the same; only the volume drawn differs. This confuses more discussions here than any other single point.

That is the shape of it. The detail is where I would expect to be corrected.

26 likes 19d

endo_fellow_rkTL313 Jul 2026#5

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Staff rationale: Hidden by community flags. Described a research-use-only compound as approved for human use after a correction earlier in this topic (R4).

Narrowing post #3, because the general version has more than one answer.

The best check on any reconstitution calculation is to do it twice by two different routes — mass per volume, then volume per dose — and see whether they agree. They should, and when they do not it is nearly always the concentration step.

The corresponding entry is in the public moderation log. Hidden posts are never deleted.

r.ekstromTL217 Jul 2026#6

Everything in post #4 holds. The case it does not cover is the one I have.

Over-dilution: if your target dose is 0.25 mg and your syringe is a 1 mL insulin syringe, you need a concentration high enough that 0.25 mg fits on the scale. A 0.25 mg/mL solution requires drawing the entire 1 mL syringe — not readable. A 5 mg/mL solution requires drawing 50 μL — also not practical on an insulin syringe.

I would rather post the uncertainty than round it away.

2 likes 11d

This topic was referenced in

Foaming during reconstitution and whether it mattersPractice › Reconstitution · 24 replies

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