someone explain units to me like I have not read a paper in years
someone explain units to me like I have not read a paper in years. Searched first, found three threads that contradict each other, hence the post.
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.
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.
The failure modes I have actually seen posted here, in order of frequency.
One: reconstituting at a different volume than intended and not writing it down, so the next draw is based on a remembered concentration. Two: treating units as a dose rather than a volume, which breaks the moment the concentration changes. Three: assuming a syringe is U-100 when it is not.
All three are solved by the same two habits — do the arithmetic before the water goes in, and write the result on the glass. Neither costs anything and between them they cover almost every question this board gets.
Tell me where this is wrong. That is the useful part of posting it.
best — the order this archive was captured in
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.
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
Are you accounting for the powder volume, or is that where the confusion is?
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
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.
Correction: that gives 20 units, not what you have written. 5mg into 1mL is 5mg/mL and the division follows from there.
reconstituting at a round concentration makes every later dose easy
I would not round that figure. At 10mg/mL a rounding error of two units is a real fraction of the intended amount.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
label the vial with the date as well as the concentration
Disagree with the "more water is safer" framing.
Right, and the arithmetic behind it: 5mg in 1mL is 5mg/mL, so 2.5mg is 50 units.
aim the stream at the glass wall, not at the cake
aim the stream at the glass wall, not at the cake
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
How many mg in the vial and how many mL are you adding?
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 0.5mg is 0.5 divided by 5 millilitres, which is 10 units.
Asked SGN what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
What is written on the vial right now?
What is written on the vial right now?
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
- 1I would not round that figure. At 10mg/mL a rounding error of two units is a…8 comments in this branch · started by u/cesar_ivaturi