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 getting two different answers.
The bit I cannot resolve on my own is 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.
Tell me what I have not thought of.
Short answer first, then the reasoning. Dead space is the answer to the missing dose. A fixed-needle insulin syringe holds a few microlitres in the hub and needle after the plunger bottoms out, and on small draws that is a measurable percentage of every dose. Across ten draws it adds up to most of an eleventh, which is exactly the "nine draws from a ten-dose vial" complaint. Luer-lock syringes are worse; low-dead-space fixed-needle designs are better.
Happy to go further on any of that.
TrialTracker_MD said:Dead space is the answer to the missing dose.
Agreed, and it is worth saying that rounding to the nearest whole unit is usually acceptable at maintenance doses and is not acceptable at the bottom of a ladder, where one unit can be a fifth of the intended dose.
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Shop Reference StandardsDr.NateNeph 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…
Same position here, arrived at the long way round. Do it in two steps and it stops being confusing. First concentration: 10mg into 2ml is 5mg/ml. Then volume: a 0.5mg dose is 0.5 ÷ 5 = 0.1ml. Then units, and this is where people go wrong — a U-100 syringe is graduated in hundredths of a millilitre, so 0.1ml is 10 units. The word "units" has nothing to do with milligrams; it is a volume marking that exists because insulin happens to come at 100 units per ml.
From the other side of the consultation, briefly.
Just received my dosing arithmetic order — packaging review:
- Outer box: plain brown, no medication identifiers (discreet) ✅
- Inner insulation: Styrofoam with 2 gel ice packs ✅
- Temperature: vials were cold to touch on arrival ✅
- Labeling: lot number, BUD, compound name, concentration ✅
- Included: COA, reconstitution instructions, dosing card ✅
This is what professional compounding pharmacy shipping looks like. If your order arrives without these basics, reconsider your vendor.