genuine question about insulin syringe that I am slightly embarrassed to ask
genuine question about insulin syringe that I am slightly embarrassed to ask. I am not trying to be the "source?" guy. I would just like a source.
The whole calculation, once, with real numbers.
You have a 5mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 1.67mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 1.5mg you need 1.5 divided by 1.67 millilitres, which is 90 units on the barrel. Write "1.67mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
The failure modes I have actually seen posted here, in order of frequency.
One: reconstituting at a different volume than intended and not writing it down, so the next draw is based on a remembered concentration. Two: treating units as a dose rather than a volume, which breaks the moment the concentration changes. Three: assuming a syringe is U-100 when it is not.
All three are solved by the same two habits — do the arithmetic before the water goes in, and write the result on the glass. Neither costs anything and between them they cover almost every question this board gets.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
Ask me anything specific. Anything general I will probably get wrong.
best — the order this archive was captured in
The arithmetic in full: concentration is mass over volume, so 30mg into 2mL gives 15mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 0.75mg is 0.75 divided by 15 millilitres, which is 5 units.
The arithmetic in full: concentration is mass over volume, so 30mg into 2mL gives 15mg/mL.
dilara_szabo has the units point exactly right. They are a volume on the barrel and nothing else.
dilara_szabo has the units point exactly right.
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Research-use-only material is not approved for human use, so treat everything in this thread as arithmetic about solutions rather than instructions for a person.
write the concentration on the vial in marker, that is the whole post
Careful — that arithmetic is wrong. 10mg in 2mL is 5mg/mL, so 1mg draws to 20 units, not what you wrote.
twice as much water halves the concentration and doubles the units for the same dose
Show the arithmetic — where did the unit figure come from?
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.