how much of what we believe about concentration actually comes from mg/mL threads
Asking properly rather than in a comment on somebody else’s thread: how much of what we believe about concentration actually comes from mg/mL threads.
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.
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.
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 2.5mg is 2.5 divided by 5 millilitres, which is 50 units.
Sceptical readings welcome. The confident ones are the ones I distrust.
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.
Spent 3 weeks confused about this until somebody drew the table for me. 10mg, 2mL, 5mg/mL, 2.5mg is 50 units. That is the whole thing.
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
Left up and flaired Explainer — the numbers in this one check out.
Left up and flaired Explainer — the numbers in this one check out.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
write the concentration on the vial in marker, that is the whole post
bacteriostatic water has the preservative, sterile water does not
bacteriostatic water has the preservative, sterile water does not
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
Reconstituted at 2mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 5mg/mL on the glass before I put the cap back.
This. Showing the working is the fastest way for somebody else to spot the mistake.
units are a volume on a U-100 syringe, not a dose
How many mg in the vial and how many mL are you adding?
do the arithmetic before you reconstitute, not while holding a syringe
reconstituting at a round concentration makes every later dose easy
more water is not more drug, it is the same drug in a bigger volume
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
Correction: that gives 20 units, not what you have written. 5mg into 1mL is 5mg/mL and the division follows from there.
swirl, never shake
Right — the volume you add is the only variable you control here, and the cake does not change it meaningfully.
if the maths gives you a fraction of a unit, change the concentration
5mg into 3mL is 1.67mg/mL, and 1.5mg of that is 90 units
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
- 1do the arithmetic before you reconstitute, not while holding a syringe9 comments in this branch · started by u/runa_cabrera
- 2Same. I got this wrong once, caught it because the units looked absurd, and…6 comments in this branch · started by u/anya_antonsen