units are the most under-discussed thing on this board
Something I keep coming back to: units are the most under-discussed thing on this board. Bacteriostatic water contains benzyl alcohol as a preservative, which is what makes repeated entry into the same vial reasonable. Plain sterile water has no preservative. If your calculation produces a fraction of a unit, the…
The whole calculation, once, with real numbers.
You have a 15mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 5mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 0.25mg you need 0.25 divided by 5 millilitres, which is 5 units on the barrel. Write "5mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
[deleted]
Show the arithmetic — where did the unit figure come from?
Small fix — a U-100 syringe is 100 units per mL. If yours is marked differently it is not U-100 and the whole calculation changes.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
anya_antonsen has the units point exactly right. They are a volume on the barrel and nothing else.