[Discussion] the mg/mL advice in here is 3 years out of date
the mg/mL advice in here is 3 years out of date. Change my mind, genuinely — I have no stake in being right about this.
The relevant figures are 3 years, and they come from the same log I have kept the whole time.
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.
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.
Tell me where this is wrong. That is the useful part of posting it.
best — the order this archive was captured in
Left up and flaired Explainer — the numbers in this one check out.
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.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
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.
What is written on the vial right now?
What is written on the vial right now?
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
What is written on the vial right now?
piotr_bruun has the units point exactly right. They are a volume on the barrel and nothing else.
How many mg in the vial and how many mL are you adding?
more water is not more drug, it is the same drug in a bigger volume
label the vial with the date as well as the concentration
dead space in the needle hub is real and it is small
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.
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.
The arithmetic in full: concentration is mass over volume, so 5mg into 1mL gives 5mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1mg is 1 divided by 5 millilitres, which is 20 units.
This. Showing the working is the fastest way for somebody else to spot the mistake.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
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.
Spent 11 weeks confused about this until somebody drew the table for me. 10mg, 1mL, 10mg/mL, 1mg is 10 units. That is the whole thing.
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.
if the maths gives you a fraction of a unit, change the concentration
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
Bacteriostatic or plain sterile water?
- 1If your calculation produces a fraction of a unit, the concentration is…6 comments in this branch · started by u/vial_math_vera