[Discussion] units are doing more work than we give it credit for
The title is the argument: units are doing more work than we give it credit for. Here is the rest of it.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
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.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
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
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.
Correction: that gives 10 units, not what you have written. 20mg into 2mL is 10mg/mL and the division follows from there.
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.
How many mg in the vial and how many mL are you adding?
Aim the stream down the wall of the vial rather than into the cake.
Right, and the arithmetic behind it: 5mg in 3mL is 1.67mg/mL, so 0.5mg is 30 units.
Asked TFC what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
Show the arithmetic — where did the unit figure come from?
write the concentration on the vial in marker, that is the whole post
Show the arithmetic — where did the unit figure come from?
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
a U-100 syringe reads 100 units to the millilitre, every time
more water is not more drug, it is the same drug in a bigger volume
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.
bacteriostatic water has the preservative, sterile water does not
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.
reconstituting at a round concentration makes every later dose easy
What concentration did you actually reconstitute at, rather than what did you intend to?
20mg into 1mL is 20mg/mL, and 5mg of that is 25 units
dead space in the needle hub is real and it is small
the powder cake sits at the bottom, the volume you add is the volume that counts
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
Right — the volume you add is the only variable you control here, and the cake does not change it meaningfully.
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.
- 1I keep a laminated card in the drawer with the arithmetic on it. Looks…12 comments in this branch · started by u/rosa_mensah