Topic summary

Converting between mg/mL and units per dose, both directions — the long version

Practice › Reconstitution reconstitution worked example syringe units dead volume concentration maths

This is a generated summary. It shows the 9 most-liked posts from a topic of 133, 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.

a.nascimentoTL2 Moderator17 Apr 2026#10

s.kravchenko, post #4: Foaming during reconstitution: bubbles in the solution are usually just air incorporated during mixing. They usually resolve with gentle warming and time. Persistent foam is unusual and might warrant contact with the supplier, but initial foam is ordinary. Go to post

Choosing a concentration on purpose rather than by accident: starting with "I want to draw 0.5 mL per dose" and working backward to the required concentration is more efficient than picking a diluent volume and hoping the math works out. State your target volume, then the required concentration follows.

27 likes in reply to #4 3mo

h.friskTL2 Moderator18 Apr 2026#14

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.

30 likes 3mo

compounding_ruthTL4Pharmacist18 Apr 2026#19

dexa_twice_yearly, post #13: I disagree with the reply above, and I think the disagreement is substantive rather than terminological. The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient. Go to post

post #18 answers the question as asked. The question underneath it is different.

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

31 likes in reply to #13 3mo

a.zamoraTL2 Moderator19 Apr 2026#31

r.mcalister, post #11: Swirling versus inverting versus leaving it alone: the vial can be gently warmed (hands around it) and swirled with a rolling motion. Vigorous shaking introduces air and can denature the peptide. Leaving it alone at room temperature usually works given enough time. Go to post

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.

27 likes in reply to #11 3mo

m.ndiayeTL2 Moderator21 Apr 2026#51

g.pemberton_uk, post #15: post #14 is right about the mechanism and I think understates the practical bit. Arithmetic step by step: a 5 mg vial with 2 mL of diluent gives (5 mg) / (2 mL) = 2.5 mg/mL. On a U-100 syringe at that concentration, 100 units = 1 mL = 2.5 mg, so each unit = 0.025 mg. A 0.25 mg dose = 0.25 / 0.025 = 10 units. Different concentration:… Go to post

33 likes in reply to #15 3mo

GDashwoodTL3Regular23 Apr 2026#85

n.hartmann, post #29: 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. Go to post

29 likes in reply to #29 3mo

m.almeidaTL2 Moderator23 Apr 2026#91

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

30 likes 3mo

KnowltonTL3Regular24 Apr 2026#104

o.vogel, post #45: Arithmetic step by step: a 5 mg vial with 2 mL of diluent gives (5 mg) / (2 mL) = 2.5 mg/mL. On a U-100 syringe at that concentration, 100 units = 1 mL = 2.5 mg, so each unit = 0.025 mg. A 0.25 mg dose = 0.25 / 0.025 = 10 units. Different concentration: different arithmetic, same principle. Go to post

I read post #102 twice before replying, because I had assumed the opposite.

Reconstituting a multi-strength kit: if a kit contains 5 mg, 10 mg, 15 mg vials and you are reconstituting all of them, writing the concentration on each vial in permanent marker as you go is the single most useful thing you can do to avoid dose errors later.

31 likes in reply to #45 3mo

r.serranoTL2 Moderator25 Apr 2026#112

n.boateng, post #16: Worth separating two things that post #12 runs together. Arithmetic step by step: a 5 mg vial with 2 mL of diluent gives (5 mg) / (2 mL) = 2.5 mg/mL. On a U-100 syringe at that concentration, 100 units = 1 mL = 2.5 mg, so each unit = 0.025 mg. A 0.25 mg dose = 0.25 / 0.025 = 10 units. Different concentration: different arithmetic, same… Go to post

29 likes in reply to #16 3mo

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Checking someone else's arithmetic: a worked example threadPractice › Reconstitution · 78 replies

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