bacteriostatic water — 16 things I got wrong before I got it right
Posting this as a discussion rather than a claim: bacteriostatic water — 16 things I got wrong before I got it right.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
Spent 24 weeks confused about this until somebody drew the table for me. 30mg, 1mL, 30mg/mL, 1.5mg is 5 units. That is the whole thing.
Ask me anything specific. Anything general I will probably get wrong.
best — the order this archive was captured in
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.
Corrected the concentration in the title, which contradicted the body. Nothing else touched.
Adding more water does not change how much peptide is in the vial.
This is the sentence that makes the rest unnecessary. Write it on the vial and the problem is gone.
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.
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 30mg into 1mL gives 30mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1.5mg is 1.5 divided by 30 millilitres, which is 5 units.
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.
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.
aim the stream at the glass wall, not at the cake
units are a volume on a U-100 syringe, not a dose
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.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
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.
Agreed on the swirl. There is no reason to shake it and a good reason not to.
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.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Show the arithmetic — where did the unit figure come from?
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.
5mg into 3mL is 1.67mg/mL, and 0.5mg 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 10mg/mL on the glass before I put the cap back.
Careful — that arithmetic is wrong. 10mg in 2mL is 5mg/mL, so 0.5mg draws to 10 units, not what you wrote.
do the arithmetic before you reconstitute, not while holding a syringe
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
swirl, never shake
Asked GGPeps what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
the powder cake sits at the bottom, the volume you add is the volume that counts
Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.
a U-100 syringe reads 100 units to the millilitre, every time
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
- 1Adding more water does not change how much peptide is in the vial. It…10 comments in this branch · started by u/hedda_ekstrom
- 2Reconstituted at 2mL when I meant to use a different volume. Caught it…7 comments in this branch · started by u/kenji_kimani