reading concentration threads from 2024 and half of it aged badly
reading concentration threads from 2024 and half of it aged badly — a position I have arrived at slowly and would like tested.
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.
Reconstituted at 1mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 30mg/mL on the glass before I put the cap back.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
I will update this if the picture changes rather than quietly leaving it up.
best — the order this archive was captured in
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.
If your calculation produces a fraction of a unit, the concentration is wrong for your dose. Change the water volume until the numbers land on whole units.
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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.
swirl, never shake
Agreed on the swirl. There is no reason to shake it and a good reason not to.
Agreed on the swirl.
This is the sentence that makes the rest unnecessary. Write it on the vial and the problem is gone.
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.
Show the arithmetic — where did the unit figure come from?
bacteriostatic water has the preservative, sterile water does not
Yes. Writing 5mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
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.
more water is not more drug, it is the same drug in a bigger volume
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
units are a volume on a U-100 syringe, not a dose
Not quite. Bacteriostatic and sterile water are not interchangeable for a multi-draw vial, and the difference is the preservative.
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 lyophilised cake displaces a small volume, so the true concentration is very slightly lower than the arithmetic suggests.
anjali_tamm has the units point exactly right. They are a volume on the barrel and nothing else.
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.
The arithmetic in full: concentration is mass over volume, so 5mg into 2mL gives 2.5mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 1mg is 1 divided by 2.5 millilitres, which is 40 units.
Careful — that arithmetic is wrong. 20mg in 2mL is 10mg/mL, so 5mg draws to 50 units, not what you wrote.
- 1If your calculation produces a fraction of a unit, the concentration is…9 comments in this branch · started by u/emeka_delgado
- 2bacteriostatic water has the preservative, sterile water does not9 comments in this branch · started by u/bruno_dumitru