unpopular opinion: most of what gets said here about dead space is guesswork
The title is the argument: unpopular opinion: most of what gets said here about dead space is guesswork. Here is the rest of it. The arithmetic in full: concentration is mass over volume, so 5mg into 1mL gives 5mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 0.75mg is 0.75 divided by 5…
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
swirl, never shake
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.
Correction: that gives 20 units, not what you have written. 5mg into 2mL is 2.5mg/mL and the division follows from there.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.