unpopular opinion: most of what gets said here about units are guesswork
Posting this as a discussion rather than a claim: unpopular opinion: most of what gets said here about units are guesswork.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one 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.
Spent 11 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.
Corrections welcome, especially the pedantic ones. Pedantry is how this board earns its reputation.
best — the order this archive was captured in
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.
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.
The arithmetic in full: concentration is mass over volume, so 10mg into 3mL gives 3.33mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 2.5mg is 2.5 divided by 3.33 millilitres, which is 75 units.
The arithmetic in full: concentration is mass over volume, so 10mg into 3mL gives 3.33mg/mL.
Right, and the arithmetic behind it: 5mg in 2mL is 2.5mg/mL, so 0.25mg is 10 units.
more water is not more drug, it is the same drug in a bigger volume
the powder cake sits at the bottom, the volume you add is the volume that counts
What concentration did you actually reconstitute at, rather than what did you intend to?
Left up and flaired Explainer — the numbers in this one check out.
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.
Careful — that arithmetic is wrong. 5mg in 1mL is 5mg/mL, so 1mg draws to 20 units, not what you wrote.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
rosa_mensah has the units point exactly right. They are a volume on the barrel and nothing else.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
reconstituting at a round concentration makes every later dose easy
aim the stream at the glass wall, not at the cake
Agreed on the swirl. There is no reason to shake it and a good reason not to.
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
the number you write down is the number you will trust at 6am
the number you write down is the number you will trust at 6am
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
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.
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.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
Asked KP what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
This. Showing the working is the fastest way for somebody else to spot the mistake.
do the arithmetic before you reconstitute, not while holding a syringe
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
- 1The lyophilised cake displaces a small volume, so the true concentration is…6 comments in this branch · started by u/viktor_kirchner