[Question] concentration — what am I missing here
Trying to get a straight answer on this: concentration — what am I missing here.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Spent 12 weeks confused about this until somebody drew the table for me. 10mg, 3mL, 3.33mg/mL, 1mg is 30 units. That is the whole thing.
Not medical advice, obviously, and nothing here is approved for human use. One person with a spreadsheet.
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.
Aim the stream down the wall of the vial rather than into the cake. Reconstitution is a solubility problem, not a mixing problem, and mechanical shear does nothing helpful.
more water is not more drug, it is the same drug in a bigger 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.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
That is sterile water, not bacteriostatic.
vial_math_vera has the units point exactly right. They are a volume on the barrel and nothing else.
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.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
write the concentration on the vial in marker, that is the whole post
Corrected the concentration in the title, which contradicted the body. Nothing else touched.
I would not round that figure. At 5mg/mL a rounding error of two units is a real fraction of the intended amount.
Correction: that gives 90 units, not what you have written. 5mg into 3mL is 1.67mg/mL and the division follows from there.
the powder cake sits at the bottom, the volume you add is the volume that counts
Asked FGP what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
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.
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.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.