the reconstitution thing finally clicked for me and I want to write it down
The title is the argument: the reconstitution thing finally clicked for me and I want to write it down. Here is the rest of it.
The arithmetic in full: concentration is mass over volume, so 10mg into 3mL gives 3.33mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 2.5mg is 2.5 divided by 3.33 millilitres, which is 75 units.
Why "more water" keeps confusing people, including me for a month.
The vial contains a fixed amount of peptide. Water changes nothing about that amount. What it changes is concentration, and concentration is the divisor between the dose you want and the volume you draw.
So doubling the water halves the concentration and doubles the units for the same dose. Nothing is diluted in any sense that matters; you are simply reading a bigger number off the same barrel. Pick the water volume that puts your usual dose on a whole number of units and life gets easier.
The whole calculation, once, with real numbers.
You have a 30mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 10mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 5mg you need 5 divided by 10 millilitres, which is 50 units on the barrel. Write "10mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
best — the order this archive was captured in
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.
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.
Spent 6 weeks confused about this until somebody drew the table for me. 10mg, 2mL, 5mg/mL, 2.5mg is 50 units. That is the whole thing.
Working has to be shown on arithmetic posts. Added a note asking for it rather than removing this one.
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.