Accepted answer
At 3.33 mg/mL a 0.25 mg dose is 7.5 units on a U-100 barrel and a 1 mg dose is 30 units. Volume is dose divided by concentration and one unit is 0.01 mL, so the unit count is dose ÷ 3.33 × 100. Both land in a readable part of the barrel, which is what choosing the volume deliberately buys you.
Start from the dose you intend to draw and work backwards to the volume that puts it in a readable part of the barrel.
The other direction: 10 mg in 3 mL is 3.33 mg/mL, and a 0.5 mg dose becomes 0.15 mL, or 15 units. More barrel, easier reading, and a larger fraction of the vial volume lost to dead space across the same number of draws.
Worked example. A 10 mg vial reconstituted with 2 mL gives 5 mg/mL. A 0.5 mg dose is 0.5 ÷ 5 = 0.1 mL, which on a U-100 syringe is 10 units. Reconstitute the same vial with 1 mL and the concentration doubles to 10 mg/mL, the same dose becomes 0.05 mL, and you are now reading 5 units instead of 10 — the same dose at half the resolution.
Insulin syringe barrel graduations are typically 1 unit on a 0.3 mL barrel, 1 unit on a 0.5 mL barrel and 2 units on a 1 mL barrel, which is why the barrel size changes what is readable.
Write the concentration on the label at reconstitution, in units per dose.
2Minor: the filter membrane chemistry matters as much as the pore size for adsorption. – e_dziedzic 33 days ago add a comment