[Discussion] mg/mL is doing more work than we give it credit for
Something I keep coming back to: mg/mL is doing more work than we give it credit for.
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.
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.
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.
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
best — the order this archive was captured in
The whole calculation, once, with real numbers.
You have a 10mg vial. You add 3mL of bacteriostatic water. Concentration is mass over volume: 3.33mg/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 3.33 millilitres, which is 15 units on the barrel. Write "3.33mg/mL" on the vial in marker before you put it away, and you never have to do this again for that vial.
Agreed on the swirl. There is no reason to shake it and a good reason not to.
the number you write down is the number you will trust at 6am
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
How many mg in the vial and how many mL are you adding?
aim the stream at the glass wall, not at the cake
the powder cake sits at the bottom, the volume you add is the volume that counts
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
reconstituting at a round concentration makes every later dose easy
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.
Working has to be shown on arithmetic posts. Added a note asking for it rather than removing this one.
more water is not more drug, it is the same drug in a bigger volume
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.
Did the maths give you a whole number of units, or a fraction?
dead space in the needle hub is real and it is small
Show the arithmetic — where did the unit figure come from?
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
units are a volume on a U-100 syringe, not a dose
- 1How many mg in the vial and how many mL are you adding?9 comments in this branch · started by u/mateusz_achebe
- 2Research-use-only material is not approved for human use, so treat…6 comments in this branch · started by u/swirl_dont_shake