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 millilitres, which is 15 units.
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 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.
Tell me where this is wrong. That is the useful part of posting it.
best — the order this archive was captured in
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?
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
bacteriostatic water has the preservative, sterile water does not
The whole calculation, once, with real numbers.
You have a 10mg vial. You add 2mL of bacteriostatic water. Concentration is mass over volume: 5mg/mL. A U-100 insulin syringe is graduated at 100 units per millilitre, so one unit is 0.01mL.
To draw 0.5mg you need 0.5 divided by 5 millilitres, which is 10 units on the barrel. Write "5mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
write the concentration on the vial in marker, that is the whole post
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.
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.
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Is that a U-100 syringe? The barrel markings change the answer completely.
What is written on the vial right now?
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
Corrected the concentration in the title, which contradicted the body. Nothing else touched.
- 1That only works if the fill weight is exactly the label weight, and it…6 comments in this branch · started by u/karl_fischer_kev