This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted 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.
The right answer here may simply be that it has not been measured.
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.
I would be glad to be shown a cleaner way of putting this.
Worth separating two things that post #89 runs together.
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.
I would hold that lightly until someone with a larger sample weighs in.
This follows post #93 rather than contradicting 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.
That is the practical version. The rigorous version is longer and says the same thing.
I read post #93 twice before replying, because I had assumed the opposite.
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.
That is one dataset and I would not build a rule on it.
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.
A guess, clearly labelled as one.
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.
Where I part company with post #97, and it is a narrow parting.
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.
Post #97 is the version of this I will quote in future. One addition.
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.
Adding it because I spent an afternoon working it out and nobody should have to twice.
Adding the measurement that post #101 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.
The mechanism is plausible, which is not the same as established.
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.
For what it is worth, the same held on the two occasions I checked.
Picking up post #104: that is the part I would want checked first.
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.
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.
Anyone who has looked at this more carefully, please correct the record.
Worth separating two things that post #106 runs together.
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.
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.
Marking that as an opinion rather than a finding.
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 reasoning is more useful than the number, which is why I have shown 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.
That is the honest state of it as of this week.
Post #112 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.
The decimal-point error: computing 5 mg / 2 mL as 0.25 mg/mL instead of 2.5 mg/mL is the most common arithmetic error in this subcategory. The habit that catches it: writing the units in every step of the calculation.
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.
The disagreement above is smaller than it looks once the terms are fixed.
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.
It is worth checking rather than assuming, which costs nothing.
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.
That is what the documentation says. What happens in practice is usually close.
Picking up post #117: that is the part I would want checked first.
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.
On post #118 — agreed on the reasoning, with one qualification.
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.