reading bacteriostatic water threads from 2024 and half of it aged badly
reading bacteriostatic water threads from 2024 and half of it aged badly. Change my mind, genuinely — I have no stake in being right about this.
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 13 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.
The whole calculation, once, with real numbers.
You have a 10mg vial. You add 2mL of bacteriostatic water. Concentration is mass over volume: 5mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 5mg you need 5 divided by 5 millilitres, which is 100 units on the barrel. Write "5mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
Screenshot none of this. Read the whole thread, including the parts where I am told I am wrong.
best — the order this archive was captured in
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.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Bacteriostatic or plain sterile water?
Show the arithmetic — where did the unit figure come from?
units are a volume on a U-100 syringe, not a dose
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.
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.
Are you accounting for the powder volume, or is that where the confusion is?
Yes. Writing 20mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
What concentration did you actually reconstitute at, rather than what did you intend to?
Correction: that gives 10 units, not what you have written. 30mg into 3mL is 10mg/mL and the division follows from there.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
the powder cake sits at the bottom, the volume you add is the volume that counts
Did the maths give you a whole number of units, or a fraction?
How many mg in the vial and how many mL are you adding?
bacteriostatic water has the preservative, sterile water does not
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
aim the stream at the glass wall, not at the cake
What is written on the vial right now?
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
I would not round that figure. At 2.5mg/mL a rounding error of two units is a real fraction of the intended amount.
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 1mg is 1 divided by 6.67 millilitres, which is 15 units.
Is that a U-100 syringe? The barrel markings change the answer completely.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
Asked WWB what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
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.
Reconstituted at 1mL 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.
- 1Adding more water does not change how much peptide is in the vial. It…11 comments in this branch · started by u/rina_bergstrom
- 2bacteriostatic water has the preservative, sterile water does not11 comments in this branch · started by u/emil_wojcik