mg/mL is the most under-discussed thing on this board
mg/mL is the most under-discussed thing on this board. Not a hot take, just something I have not seen said plainly here.
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.
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 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.
That is everything I have. The rest is opinion and I have tried to keep it out.
best — the order this archive was captured in
The whole calculation, once, with real numbers.
You have a 10mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 3.33mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 2mg you need 2 divided by 3.33 millilitres, which is 60 units on the barrel. Write "3.33mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
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.
Yes. Writing 10mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
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.
This. Showing the working is the fastest way for somebody else to spot the mistake.
Left up and flaired Explainer — the numbers in this one check out.
Right — the volume you add is the only variable you control here, and the cake does not change it meaningfully.
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a U-100 syringe reads 100 units to the millilitre, every time
Reconstituted at 3mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 3.33mg/mL on the glass before I put the cap back.
Show the arithmetic — where did the unit figure come from?
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
What is written on the vial right now?
How many mg in the vial and how many mL are you adding?
do the arithmetic before you reconstitute, not while holding a syringe
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.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
Did the maths give you a whole number of units, or a fraction?
The arithmetic in full: concentration is mass over volume, so 10mg into 1mL gives 10mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 2.5mg is 2.5 divided by 10 millilitres, which is 25 units.
Is that a U-100 syringe? The barrel markings change the answer completely.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
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.
- 1If your calculation produces a fraction of a unit, the concentration is…7 comments in this branch · started by u/sigrid_kaufmann
- 2The whole calculation, once, with real numbers. You have a 10mg vial. You…6 comments in this branch · started by u/units_not_mg