Accepted answer
At 4 mg/mL a 0.25 mg draw is 6.3 units on a U-100 barrel and a 2.4 mg draw is 60. Those two numbers decide it, because the concentration is only sensible relative to the smallest and largest volumes you will actually measure with it. Both land on a readable part of a U-100 barrel, which is the entire point of choosing the diluent volume deliberately rather than pouring in a round number. The other consideration is time: a vial you will finish in a fortnight can be concentrated, and a vial you will draw from for months should be split at reconstitution instead.
Aim for a dose volume somewhere between about 10 and 30 units on a U-100 barrel and the reading problem disappears.
Vial headspace is the hard constraint. A nominal 2 mL vial typically holds a little over 2 mL to the shoulder; adding 3 mL is not an option and attempting it wastes the lot.
Round to a diluent volume you can measure accurately. Measuring 1.00 mL on a 1 mL syringe is reliable; measuring 1.37 mL on anything is not, and the error propagates into every dose.
Published content assay results across the independent testing services show nominal and measured content differing by one to ten per cent, which makes content the dominant term in dose error.
Nothing here is medical advice, and research-use material is not approved for human use.
Measure a volume you can actually measure. Round numbers, real syringes.
I have seen exactly this failure mode twice and both times it was the diluent volume. – nils_karlberg 2 months ago add a comment