Converting between mg/mL and units per dose, both directions
Coming back to post #2, because the follow-up matters more than the original answer.
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.
Confirming post #9 from a second method, which matters more than confirming it from a second person.
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.
Adding it in case it saves somebody the afternoon it cost me.
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.
Everything in post #46 holds. The case it does not cover is the one I have.
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.
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 strength of my opinion here exceeds the strength of my evidence.
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