help me understand concentration, I have read the wiki twice
Asking properly rather than in a comment on somebody else’s thread: help me understand concentration, I have read the wiki twice.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
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.
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
best — the order this archive was captured in
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.
Spent 10 weeks confused about this until somebody drew the table for me. 5mg, 2mL, 2.5mg/mL, 1mg is 40 units. That is the whole thing.
aim the stream at the glass wall, not at the cake
What is written on the vial right now?
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.
Yes. Writing 2.5mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
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How many mg in the vial and how many mL are you adding?
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
a U-100 syringe reads 100 units to the millilitre, every time
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.
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
Same.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
write the concentration on the vial in marker, that is the whole post
Right — the volume you add is the only variable you control here, and the cake does not change it meaningfully.