cored the stopper on day 9. rotate your puncture site
Something I keep coming back to: cored the stopper on day 9. rotate your puncture site.
Asked SSA what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
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.
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.
Please do not ask me what dose you should be on. I genuinely do not know and neither does anyone else here.
best — the order this archive was captured in
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.
Right — the volume you add is the only variable you control here, and the cake does not change it meaningfully.
Spent 3 weeks confused about this until somebody drew the table for me. 20mg, 3mL, 6.67mg/mL, 5mg is 75 units. That is the whole thing.
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
The whole calculation, once, with real numbers.
You have a 10mg vial. You add 2mL 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 2.5mg you need 2.5 divided by 5 millilitres, which is 50 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.
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 failure modes I have actually seen posted here, in order of frequency.
reflux_report has the units point exactly right. They are a volume on the barrel and nothing else.
twice as much water halves the concentration and doubles the units for the same dose
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
the powder cake sits at the bottom, the volume you add is the volume that counts
do the arithmetic before you reconstitute, not while holding a syringe
How many mg in the vial and how many mL are you adding?