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…
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