genuine question about mg/mL that I am slightly embarrassed to ask
Asking properly rather than in a comment on somebody else’s thread: genuine question about mg/mL that I am slightly embarrassed to ask.
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 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.
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.
Correction: that gives 50 units, not what you have written. 30mg into 3mL is 10mg/mL and the division follows from there.
Bacteriostatic or plain sterile water?
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
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.
swirl, never shake
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
What concentration did you actually reconstitute at, rather than what did you intend to?
reconstituting at a round concentration makes every later dose easy
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
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.
Shook the first vial because nobody told me not to.
Disagreeing with this line only: adding more water is not a safety margin, it is a different divisor.
bacteriostatic water has the preservative, sterile water does not
units are a volume on a U-100 syringe, not a dose
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I would not round that figure. At 1.67mg/mL a rounding error of two units is a real fraction of the intended amount.
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.
This is the sentence that makes the rest unnecessary. Write it on the vial and the problem is gone.
Pushback on the syringe advice: a U-100 barrel reads units of volume. Calling them "doses" is how the confusion starts.
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.
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.
Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.
Careful — that arithmetic is wrong. 15mg in 3mL is 5mg/mL, so 0.75mg draws to 15 units, not what you wrote.
Careful — that arithmetic is wrong.
Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.
- 1Shook the first vial because nobody told me not to. It was fine, but I have…10 comments in this branch · started by u/rina_bergstrom