[Question] mg/mL — what am I missing here
Slightly embarrassed to be asking this, but: mg/mL — 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…
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.
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
[deleted]
a U-100 syringe reads 100 units to the millilitre, every time
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
dead space in the needle hub is real and it is small
The lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests.
This is the sentence that makes the rest unnecessary. Write it on the vial and the problem is gone.
the powder cake sits at the bottom, the volume you add is the volume that counts
10mg into 1mL is 10mg/mL, and 1mg of that is 10 units
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.
This. Showing the working is the fastest way for somebody else to spot the mistake.
do the arithmetic before you reconstitute, not while holding a syringe
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.