InsuranceTom said:

Do it in two steps and it stops being confusing.

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.

pete_manc_UK 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…

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.

NurseKim_ATL said:

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

Sharing my dosing arithmetic titration experience with compounded semaglutide — I have been tracking injection volumes meticulously:

Using 5mg/2mL concentration with 1cc insulin syringes:

• Month 1: 10 units (0.25mg) — mild appetite reduction
• Month 2: 20 units (0.5mg) — significant appetite suppression
• Month 3: 30 units (0.75mg) — custom intermediate dose
• Month 4: 40 units (1.0mg) — optimal for me, staying here

The beauty of compounded vials is you can do custom intermediate doses. My provider was great about tailoring to my response.

A narrower follow-up, since the general answer is now clear:

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?

Closing the loop on my own question.

Resolved. I wrote mg, ml and mg/ml on the vial in marker and did the division in that order, and the two of us now get the same number every time.