[Discussion] the insulin syringe advice in here is 2 years out of date
the insulin syringe advice in here is 2 years out of date, and I am aware this is a minority view on this board.
The numbers the title promised, since a headline without them is worthless: 2 years. Everything below is context for those.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
The dead space question sent me down a rabbit hole for a week. It is a fraction of a unit and it is the same every draw.
If two or three other people have done the same thing we might actually learn something. Alone it is an anecdote.
best — the order this archive was captured in
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Adding more water does not change how much peptide is in the vial. It changes the concentration, which changes the volume you draw for the same amount. That is the entire relationship.
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This. Showing the working is the fastest way for somebody else to spot the mistake.
The arithmetic in full: concentration is mass over volume, so 20mg into 2mL gives 10mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 5mg is 5 divided by 10 millilitres, which is 50 units.
Spent 18 weeks confused about this until somebody drew the table for me. 20mg, 3mL, 6.67mg/mL, 2mg is 30 units. That is the whole thing.
if the maths gives you a fraction of a unit, change the concentration
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.
twice as much water halves the concentration and doubles the units for the same dose
The arithmetic in full: concentration is mass over volume, so 20mg into 2mL gives 10mg/mL.
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
Yes. Writing 30mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
Careful — that arithmetic is wrong. 15mg in 3mL is 5mg/mL, so 0.25mg draws to 5 units, not what you wrote.
aim the stream at the glass wall, not at the cake
Asked SGN what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
Left up and flaired Explainer — the numbers in this one check out.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
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.
Reconstituted at 1mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 15mg/mL on the glass before I put the cap back.
I would not round that figure. At 5mg/mL a rounding error of two units is a real fraction of the intended amount.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
Bacteriostatic or plain sterile water?
Bacteriostatic or plain sterile water?
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
Correction: that gives 5 units, not what you have written. 15mg into 1mL is 15mg/mL and the division follows from there.
The lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests. It is a fraction of a percent and it is dwarfed by fill tolerance.
- 1The arithmetic in full: concentration is mass over volume, so 20mg into 2mL…7 comments in this branch · started by u/quarter_dose_queen