[Discussion] can we stop arguing about dead space until somebody posts a number
can we stop arguing about dead space until somebody posts a number. I would rather ask a basic question now than get this wrong quietly for two months.
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.
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.
That is everything I have. The rest is opinion and I have tried to keep it out.
best — the order this archive was captured in
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.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
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.
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
Correction: that gives 30 units, not what you have written. 20mg into 3mL is 6.67mg/mL and the division follows from there.
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.
I would not round that figure. At 20mg/mL a rounding error of two units is a real fraction of the intended amount.
Reconstituted at 2mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 2.5mg/mL on the glass before I put the cap back.
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 5mg is 5 divided by 5 millilitres, which is 100 units.
Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.
30mg into 3mL is 10mg/mL, and 2.5mg of that is 25 units
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