[Question] dead space — what am I missing here
dead space — what am I missing here. I would rather ask a basic question now than get this wrong quietly for two months.
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 contains benzyl alcohol as a preservative, which is what makes repeated entry into the same vial reasonable. Plain sterile water has no 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.
That is everything I have. The rest is opinion and I have tried to keep it out.
best — the order this archive was captured in
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.
5mg into 2mL is 2.5mg/mL, and 1mg of that is 40 units
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.
aim the stream at the glass wall, not at the cake
do the arithmetic before you reconstitute, not while holding a syringe
Wrote the date on the vial as well as the concentration after losing track of which one was opened first.
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 30mg into 3mL gives 10mg/mL. A U-100 syringe is graduated at 100 units per millilitre, so 2mg is 2 divided by 10 millilitres, which is 20 units.
This. Showing the working is the fastest way for somebody else to spot the mistake.
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.
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Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
What concentration did you actually reconstitute at, rather than what did you intend to?
What concentration did you actually reconstitute at, rather than what did you intend to?
erez_perrin has the units point exactly right. They are a volume on the barrel and nothing else.
Same. I got this wrong once, caught it because the units looked absurd, and have written on every vial since.
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.
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
label the vial with the date as well as the concentration
Did the maths give you a whole number of units, or a fraction?
Bacteriostatic or plain sterile water?
Agreed — units are volume.
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.
Agreed on the swirl. There is no reason to shake it and a good reason not to.
reconstituting at a round concentration makes every later dose easy
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