unpopular opinion: most of what gets said here about mg/mL is guesswork
unpopular opinion: most of what gets said here about mg/mL is guesswork, and I am aware this is a minority view on this board.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
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.
Research-use-only material is not approved for human use and nothing here should be read as a recommendation to use it.
best — the order this archive was captured in
The whole calculation, once, with real numbers.
You have a 5mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 1.67mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 1.5mg you need 1.5 divided by 1.67 millilitres, which is 90 units on the barrel. Write "1.67mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
the number you write down is the number you will trust at 6am
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
The arithmetic in full: concentration is mass over volume, so 20mg into 3mL gives 6.67mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 2mg is 2 divided by 6.67 millilitres, which is 30 units.
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.
Reconstituted at 2mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 5mg/mL on the glass before I put the cap back.
Correcting myself above: I wrote the concentration the wrong way up. Mass over volume, not volume over mass.
do the arithmetic before you reconstitute, not while holding a syringe
Right — the volume you add is the only variable you control here, and the cake does not change it meaningfully.
Small fix — a U-100 syringe is 100 units per mL. If yours is marked differently it is not U-100 and the whole calculation changes.
- 1The whole calculation, once, with real numbers. You have a 5mg vial. You add…6 comments in this branch · started by u/karl_fischer_kev