Adding the numbers, since they settle part of this. The three numbers to write on the vial: total mg, total ml, and mg per ml. Everything else is division. And the sanity check is that dose volume times number of doses should be less than the volume you put in, because dead space takes the difference.
Following on from Dr.LeslieOBGYN — and this may be the naive question:
How much material I am losing to dead space, and whether that explains why a 10mg vial gives me nine usable draws rather than ten?
Dr.PeteFamMed said:The three numbers to write on the vial: total mg, total ml, and mg per ml.
Coming at Dr.PeteFamMed’s question from a different direction. Concentration choice is a precision decision, not a preference. Reconstitute high and every dose is a tiny volume where one unit of syringe error is a large fraction of the dose. Reconstitute low and you get more graduations per dose, so the same hand tremor costs proportionally less. Against that, more diluent means more benzyl alcohol and a shorter comfortable in-use window.
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Browse GL BiochemOP back with an update, since a thread like this is useless without one.
My error was treating units as a mass. Once I wrote mg/ml on the vial in marker and worked in millilitres first, the two of us got the same answer.
PedsEndoPhilly said:Concentration choice is a precision decision, not a preference.
Agreed, and it is worth saying that rounding to the nearest whole unit is usually acceptable at maintenance doses and is not acceptable at the bottom of a ladder, where one unit can be a fifth of the intended dose.