the dead space question that gets asked weekly, answered properly
the dead space question that gets asked weekly, answered properly. It is the sort of thing everyone half-believes and nobody writes down.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Asked MKM what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
Why "more water" keeps confusing people, including me for a month.
The vial contains a fixed amount of peptide. Water changes nothing about that amount. What it changes is concentration, and concentration is the divisor between the dose you want and the volume you draw.
So doubling the water halves the concentration and doubles the units for the same dose. Nothing is diluted in any sense that matters; you are simply reading a bigger number off the same barrel. Pick the water volume that puts your usual dose on a whole number of units and life gets easier.
If somebody has the same thing measured a different way, post it next to mine and we will see whether they agree.
best — the order this archive was captured in
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.
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.
The lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests.
Right, and the arithmetic behind it: 20mg in 2mL is 10mg/mL, so 2mg is 20 units.
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.
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.
Show the arithmetic — where did the unit figure come from?
units are a volume on a U-100 syringe, not a dose
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
twice as much water halves the concentration and doubles the units for the same dose
Reconstituted at 3mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 6.67mg/mL on the glass before I put the cap back.
if the maths gives you a fraction of a unit, change the concentration
label the vial with the date as well as the concentration
write the concentration on the vial in marker, that is the whole post
Spent 15 weeks confused about this until somebody drew the table for me. 15mg, 3mL, 5mg/mL, 0.25mg is 5 units. That is the whole thing.
The arithmetic in full: concentration is mass over volume, so 15mg into 3mL gives 5mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 0.75mg is 0.75 divided by 5 millilitres, which is 15 units.
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
Reminder: this board does maths, not dosing.
vial_math_vera has the units point exactly right. They are a volume on the barrel and nothing else.
vial_math_vera has the units point exactly right.
This is the sentence that makes the rest unnecessary. Write it on the vial and the problem is gone.
- 1Not quite. Bacteriostatic and sterile water are not interchangeable for a…6 comments in this branch · started by u/sigrid_kaufmann