RetaRick_CA said:

Concentration choice is a precision decision, not a preference.

I am going to disagree with reconstituting low as a general rule. More diluent, more punctures, more in-use days at room temperature, and the stability trade-off is real. Precision is not the only variable being optimised.

hannah_MT said:

I reconstituted a 10mg vial with 2ml of bacteriostatic water and I want someone to check my unit arithmetic before I draw anything, because I keep…

For anyone reconstituting dosing arithmetic peptides: the water-to-powder ratio determines your concentration. Here's my reference:

More water = easier to measure small doses but vial runs out faster. Find the balance that works for your dose.

Dr.PeteFamMed said:

I am going to disagree with reconstituting low as a general rule.

Compounding pharmacy dose accuracy check for dosing arithmetic: I always verify my first dose from a new vial by weighing it on a milligram scale. Draw up your dose, weigh the syringe, subtract empty syringe weight, compare to expected water weight at that volume.

For a 10-unit dose (0.1mL): expected weight ~100mg of water. If it's significantly off, your syringe may be inaccurate. Cheap insulin syringes can have ±5% volume accuracy. Spring for quality brands like BD or Terumo.

Following on from ZaraB_AL — 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?

Reporting back.

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.