dead space is the most under-discussed thing on this board
dead space is the most under-discussed thing on this board, and I am aware this is a minority view on this board. The whole calculation, once, with real numbers. You have a 5mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 1.67mg/mL. A U-100 insulin syringe is graduated at 100 units…
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.
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
Careful — that arithmetic is wrong. 10mg in 3mL is 3.33mg/mL, so 2.5mg draws to 75 units, not what you wrote.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
Are you accounting for the powder volume, or is that where the confusion is?
if the maths gives you a fraction of a unit, change the concentration