[Explainer] units are volume, mg are mass, this is the #1 error on this site
units are volume, mg are mass, this is the #1 error on this site. It comes up every few weeks and the answer has not changed.
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 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.
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.
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
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.
Bacteriostatic water contains benzyl alcohol as a preservative, which is what makes repeated entry into the same vial reasonable.
Right, and the arithmetic behind it: 30mg in 2mL is 15mg/mL, so 0.75mg is 5 units.
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.
Correction: that gives 40 units, not what you have written. 5mg into 1mL is 5mg/mL and the division follows from there.
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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.
Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.
label the vial with the date as well as the concentration
aim the stream at the glass wall, not at the cake
a U-100 syringe reads 100 units to the millilitre, every time
Shook the first vial because nobody told me not to. It was fine, but I have swirled every one since.
Bacteriostatic or plain sterile water?
That is sterile water, not bacteriostatic. Same appearance, different product, and it matters for a multi-draw vial.
Did the maths give you a whole number of units, or a fraction?
Working has to be shown on arithmetic posts. Added a note asking for it rather than removing this one.
This. Showing the working is the fastest way for somebody else to spot the mistake.
the number you write down is the number you will trust at 6am
Is that a U-100 syringe? The barrel markings change the answer completely.
Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.
twice as much water halves the concentration and doubles the units for the same dose
- 1The arithmetic in full: concentration is mass over volume, so 5mg into 2mL…8 comments in this branch · started by u/bac_water_bandit
- 2Did the maths give you a whole number of units, or a fraction?7 comments in this branch · started by u/saskia_mwangi