[Question] reconstitution — what am I missing here
reconstitution — what am I missing here. If this has been answered properly somewhere, link me and I will delete.
The dead space question sent me down a rabbit hole for a week. It is a fraction of a unit and it is the same every draw.
Spent 14 weeks confused about this until somebody drew the table for me. 10mg, 3mL, 3.33mg/mL, 1mg is 30 units. That is the whole thing.
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 5mg you need 5 divided by 5 millilitres, which is 100 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.
Screenshot none of this. Read the whole thread, including the parts where I am told I am wrong.
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.
Left up and flaired Explainer — the numbers in this one check out.
What is written on the vial right now?
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 2mg is 2 divided by 5 millilitres, which is 40 units.
label the vial with the date as well as the concentration
Small fix — a U-100 syringe is 100 units per mL. If yours is marked differently it is not U-100 and the whole calculation changes.
more water is not more drug, it is the same drug in a bigger volume
Is that a U-100 syringe? The barrel markings change the answer completely.
I would not round that figure. At 20mg/mL a rounding error of two units is a real fraction of the intended amount.
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
Not quite.
Right, and the arithmetic behind it: 15mg in 3mL is 5mg/mL, so 0.5mg is 10 units.
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
Bacteriostatic or plain sterile water?
bacteriostatic water has the preservative, sterile water does not
Agreed on the swirl. There is no reason to shake it and a good reason not to.
Agreed on the swirl.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
bacteriostatic water has the preservative, sterile water does not
dilara_szabo has the units point exactly right. They are a volume on the barrel and nothing else.
if the maths gives you a fraction of a unit, change the concentration
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.
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.
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.
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.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
Careful — that arithmetic is wrong. 15mg in 3mL is 5mg/mL, so 0.75mg draws to 15 units, not what you wrote.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
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.
twice as much water halves the concentration and doubles the units for the same dose
Are you accounting for the powder volume, or is that where the confusion is?
- 1bacteriostatic water has the preservative, sterile water does not12 comments in this branch · started by u/dilara_szabo
- 2What is written on the vial right now?7 comments in this branch · started by u/emil_zamora