This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
No notes. Posting so the count is not one.
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.
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 checking against a second source before it gets quoted onward.
Post #63 answers the question as asked. The question underneath it is different.
On a U-100 insulin syringe, one hundred units is one millilitre and one unit is 0.01 millilitres. Units are volume marks. They mean nothing until you know the concentration.
That is my reading. Someone else read the same page differently and was reasonable.
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.
Dead volume is the part nobody mentions until it costs them a dose. A fixed-needle insulin syringe holds very little; a detachable-needle luer configuration can hold enough to matter at small doses.
Everything in post #63 holds. The case it does not cover is the one I have.
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.
That is all the detail I have. Someone else will have more.
Narrowing post #67, because the general version has more than one answer.
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 am describing what is, rather than arguing for what should be.
A 0.3 mL barrel has more space between graduations than a 1 mL barrel for the same volume, which is the entire practical argument for the smaller syringe. Resolution, not capacity.
Adding the measurement that post #67 says would settle it.
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.
It reads as pedantry until the day it does not.
Adding thanks rather than a view. I do not have a view worth the space.
Post #68 describes the usual case. This is about the unusual one.
Working out the concentration after the fact from the volume you added is fine. Working it out from the volume you meant to add is where the errors come from — read the barrel, not the plan.
If this contradicts something upthread, the upthread version may well be the better one.
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.
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.
Answering the question post #72 raises rather than the one it answers.
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.
It took me longer than it should have to see that.
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.
I would rather be precise about what I do not know than vague about what I do.
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.
One of those cases where knowing the mechanism does not help the decision.
Grateful for the specificity. Vague answers to this question are what sent me looking.
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.
Speaking for myself and not for anyone else who has posted here.
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.
Not the whole picture, but the part of it I can speak to.
Post #81 put the caveat in the right place and I want to underline it.
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.
Building on post #81 rather than restating it.
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.
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.
Post #85 and I disagree about the size of the effect, not about the direction.
Dead volume is the part nobody mentions until it costs them a dose. A fixed-needle insulin syringe holds very little; a detachable-needle luer configuration can hold enough to matter at small doses.
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.
If it helps: the failure mode here is usually boring rather than dramatic.
On post #85 — agreed on the reasoning, with one qualification.
A 0.3 mL barrel has more space between graduations than a 1 mL barrel for the same volume, which is the entire practical argument for the smaller syringe. Resolution, not capacity.