Worth separating 5 mg vial as a question about the compound from 5 mg vial as a question about the documentation. They get answered by different people and only one of them is answerable here.
A 5 mg vial and a 0.25 mg dose: the arithmetic in full Writing it up because I had to work it out twice and would rather nobody else did.
5 mg vial: setting out the arithmetic in full, because I have had to do it twice and I would rather nobody else did.
Every step is shown. If the answer is wrong the error will be visible, which is the point of writing it out rather than posting the result.
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.
Worth separating 5 mg vial as a question about the compound from 5 mg vial as a question about the documentation. They get answered by different people and only one of them is answerable here.
Appreciated. The plain phrasing does more work here than a longer post would.
Where I part company with the opening post, and it is a narrow parting.
Worked example, since the arithmetic is the whole question. Five milligrams into one millilitre is 5 mg/mL. A 0.25 mg dose is 0.05 mL, which is five units on a U-100 syringe. Check that against your own numbers rather than taking mine.
Written quickly, so the reasoning may be tighter than the wording.
Post #5 is the version of this I will quote in future. One addition.
Swirling until fully clear before drawing is worth the extra minute. A partially dissolved preparation is not uniform and the first dose out of it is not the same as the last.
Noting that the question and the thing people usually mean by it are different.
Why "add 2 mL" is not an instruction: the powder in the vial takes up space. "Add 2 mL to a 10 mL vial" and "add 2 mL of diluent so the final volume is approximately 2 mL" are different instructions. Stating the final target volume is clearer than stating the diluent added.
Not a conclusion. A place to stand while looking for one.
Helpful, and easy to find again, which is half of what a good reply is.
Post #8 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.
Correct me on the arithmetic if it is wrong; I would rather know.
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.
Everything in post #8 holds. The case it does not cover is the one I have.
5 mg vial has been discussed here with more heat than it deserves, mostly because two definitions have been in play the whole time.
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.
If this contradicts something upthread, the upthread version may well be the better one.
A vial that will not fully dissolve: check in order: is the diluent genuinely room temperature (some preservatives crystallise in cold), is the vial being warmed gently rather than shaken hard, is the injection technique clean, is the vial integrity intact. Work through that checklist before concluding the powder is insoluble.
The rule of thumb is fine; the edge cases are where it earns its keep.
The arithmetic in post #14 is right; the assumption feeding it is the part to check.
On 5 mg vial, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.
If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.
Answering the question post #12 raises rather than the one it answers.
Write the reconstitution date and the concentration on the vial. Not on a note, on the vial. Every account here of a dosing error involving the wrong concentration involves a vial with nothing written on it.
The part I am sure of is shorter than the part I have written.
Marking my place. If it changes for me I will come back and say so.
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.
Reconstituting the whole vial when you will use a quarter of it is a decision to store the rest in solution, which is the least stable state it will ever be in. Sometimes that is the right trade and it should be a decision.
If that is already documented somewhere, ignore me and link it.
Second this, and I would have said it less carefully.
Post #18 describes the usual case. This is about the unusual one.
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.
A guess, clearly labelled as one.
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.
I would not lead a decision with this, but I would not ignore it either.
Filter needles are worth considering if you are drawing from a glass ampoule and are pointless overhead for a stoppered vial. The trade is dead volume against particulate risk.
The question underneath 5 mg vial is usually "how would I tell?" rather than "what is true?", and that one has a method attached to it.
Write down what you would expect to see under each hypothesis before you collect anything. If they predict the same observation, collecting it will not help.
Answering the question post #21 raises rather than the one it answers.
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.
Adding it because I spent an afternoon working it out and nobody should have to twice.
The arithmetic in post #25 is right; the assumption feeding it is the part to check.
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.
The claim is narrower than it sounds, and deliberately so.
No notes. Posting so the count is not one.
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.
Narrowing post #29, because the general version has more than one answer.
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.
This is the sort of thing the wiki should carry and currently does not.