someone explain mg/mL to me like I have not read a paper in years
someone explain mg/mL to me like I have not read a paper in years. I am not trying to be the "source?" guy. I would just like a source.
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.
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.
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
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Corrected the concentration in the title, which contradicted the body. Nothing else touched.
write the concentration on the vial in marker, that is the whole post
reconstituting at a round concentration makes every later dose easy
Is that a U-100 syringe? The barrel markings change the answer completely.
more water is not more drug, it is the same drug in a bigger volume
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.
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
Agreed — units are volume.
Right, and the arithmetic behind it: 15mg in 2mL is 7.5mg/mL, so 1.5mg is 20 units.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
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.
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
bacteriostatic water has the preservative, sterile water does not
This. Showing the working is the fastest way for somebody else to spot the mistake.
This.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
do the arithmetic before you reconstitute, not while holding a syringe
Agreed on the swirl. There is no reason to shake it and a good reason not to.
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label the vial with the date as well as the concentration
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.
Bacteriostatic or plain sterile water?
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
Spent 21 weeks confused about this until somebody drew the table for me. 15mg, 3mL, 5mg/mL, 0.25mg is 5 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 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.
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.
10mg into 3mL is 3.33mg/mL, and 1mg of that is 30 units
Reconstituted at 2mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 7.5mg/mL on the glass before I put the cap back.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
- 1I keep a laminated card in the drawer with the arithmetic on it. Looks…11 comments in this branch · started by u/honest_syringe_2025
- 2bacteriostatic water has the preservative, sterile water does not7 comments in this branch · started by u/ines_lindqvist