[Meta] proposal — a flair for concentration posts
Housekeeping: proposal — a flair for concentration posts.
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.
The arithmetic in full: concentration is mass over volume, so 5mg into 1mL gives 5mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1.5mg is 1.5 divided by 5 millilitres, which is 30 units.
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.
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
best — the order this archive was captured in
If your calculation produces a fraction of a unit, the concentration is wrong for your dose. Change the water volume until the numbers land on whole units.
Show the arithmetic — where did the unit figure come from?
Agreed on the swirl. There is no reason to shake it and a good reason not to.
Show the arithmetic — where did the unit figure come from?
Right, and the arithmetic behind it: 5mg in 2mL is 2.5mg/mL, so 1mg is 40 units.
write the concentration on the vial in marker, that is the whole post
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.
The dead space question sent me down a rabbit hole for a week.
janek_ferrari has the units point exactly right. They are a volume on the barrel and nothing else.
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
if the maths gives you a fraction of a unit, change the concentration
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.
Yes. Writing 10mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
What concentration did you actually reconstitute at, rather than what did you intend to?