[Question] bacteriostatic water — what am I missing here
Slightly embarrassed to be asking this, but: bacteriostatic water — what am I missing here.
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.
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.
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.
Would rather be corrected in public than confident in private.
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.
Is that a U-100 syringe? The barrel markings change the answer completely.
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.
the number you write down is the number you will trust at 6am
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.
Working has to be shown on arithmetic posts. Added a note asking for it rather than removing this one.
The lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests.
kavya_radich has the units point exactly right. They are a volume on the barrel and nothing else.
Yes. Writing 5mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.
The failure modes I have actually seen posted here, in order of frequency.
One: reconstituting at a different volume than intended and not writing it down, so the next draw is based on a remembered concentration. Two: treating units as a dose rather than a volume, which breaks the moment the concentration changes. Three: assuming a syringe is U-100 when it is not.
All three are solved by the same two habits — do the arithmetic before the water goes in, and write the result on the glass. Neither costs anything and between them they cover almost every question this board gets.
Are you accounting for the powder volume, or is that where the confusion is?
Spent 11 weeks confused about this until somebody drew the table for me. 10mg, 1mL, 10mg/mL, 2mg is 20 units. That is the whole thing.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.