Accepted answer
It gives 2 mg/mL, and whether that is sensible depends on the dose you will draw from it. 5 ÷ 2.5 = 2 mg/mL in bacteriostatic water. A 0.5 mg dose is then 25 units on a U-100 barrel and a 1 mg dose is 50 units. Both land in a readable part of the barrel, which is the whole point of choosing the volume deliberately.
On the detail: this is the one decision in the whole preparation sequence that cannot be revised later, which is why it is worth thirty seconds of arithmetic.
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.
Reading a lyophilised cake
| Appearance | Interpretation | Action |
|---|
| Intact opaque puck, proud of base | Cycle ran correctly | Proceed |
| Slumped to one side | Shipped before fully dry, or vibration | Usually usable; note it |
| Glassy translucent film | Collapse above glass transition | Test before use |
| Melt-back ring at stopper | Thermal excursion in transit | Test before use |
| No visible cake at all | Very low fill, or nothing there | Weigh it; query the supplier |
Write the concentration and the resulting units-per-dose on the vial label at reconstitution. The arithmetic that is obvious now will not be obvious at six in the morning three weeks from now.
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.
Do not change the diluent volume between vials of a titration without recalculating; it is the commonest source of a ten-fold error.
Measure a volume you can actually measure. Round numbers, real syringes.
Would this be different for a peptide that foams? Mine does and I have never known why. – tobias_maartens 10 months ago add a comment