the bacteriostatic water question that gets asked weekly, answered properly
the bacteriostatic water question that gets asked weekly, answered properly. Change my mind, genuinely — I have no stake in being right about this.
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.
Asked SWB what volume they reconstitute to for their own stability testing and they answered in one line. Useful thing to know.
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.
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
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.
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.
5mg into 3mL is 1.67mg/mL, and 1.5mg of that is 90 units
reconstituting at a round concentration makes every later dose easy
write the concentration on the vial in marker, that is the whole post
Careful — that arithmetic is wrong. 10mg in 2mL is 5mg/mL, so 2mg draws to 40 units, not what you wrote.
Yes, and the dead-space point is worth repeating: it is small, it is real, and it is the same for every draw.
Yes. Writing 5mg/mL on the vial takes four seconds and removes the entire class of error this board exists to fix.
Yes.
This is the sentence that makes the rest unnecessary. Write it on the vial and the problem is gone.
units are a volume on a U-100 syringe, not a dose
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
Reminder: this board does maths, not dosing. Nobody here tells another member what amount to take.
The arithmetic in full: concentration is mass over volume, so 5mg into 3mL gives 1.67mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 0.75mg is 0.75 divided by 1.67 millilitres, which is 45 units.
aim the stream at the glass wall, not at the cake
Right — the volume you add is the only variable you control here, and the cake does not change it meaningfully.
This. Showing the working is the fastest way for somebody else to spot the mistake.
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.
Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.
the number you write down is the number you will trust at 6am
label the vial with the date as well as the concentration
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.
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
Research-use-only material is not approved for human use, so treat everything in this thread as arithmetic about solutions rather than instructions for a person.
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.
Research-use-only material is not approved for human use, so treat everything in this thread as arithmetic about solutions rather than instructions fo
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
Is that a U-100 syringe? The barrel markings change the answer completely.
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.
I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.
a U-100 syringe reads 100 units to the millilitre, every time
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