Two of us with identical vials and identical diluent arrived at different unit counts, which means one of us has a conceptual error rather than a rounding error.
Writing it up rather than posting a verdict, because a verdict is not checkable and the detail is.
The three numbers to write on the vial: total mg, total ml, and mg per ml. Everything else is division. And the sanity check is that dose volume times number of doses should be less than the volume you put in, because dead space takes the difference.
The arithmetic is right and one caveat matters: a U-40 syringe changes the markings, not the volumes. If someone hands you U-40 and you read it as U-100 you will be 2.5 times out, and that error has a direction — it is always an overdose.
The narrow version of the question 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. Not looking for reassurance. Looking for the part I have got wrong.
LarryQC_SD said:Two of us with identical vials and identical diluent arrived at different unit counts, which means one of us has a conceptual error rather than a…
Agreeing with LarryQC_SD, and the qualification matters more than the agreement. Concentration choice is a precision decision, not a preference. Reconstitute high and every dose is a tiny volume where one unit of syringe error is a large fraction of the dose. Reconstitute low and you get more graduations per dose, so the same hand tremor costs proportionally less. Against that, more diluent means more benzyl alcohol and a shorter comfortable in-use window.
LarryQC_SD said:Two of us with identical vials and identical diluent arrived at different unit counts, which means one of us has a conceptual error rather than a…
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.
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Browse GL BiochemAnswering the narrow version, because the broad one does not have a single answer. 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.
Correct me if the detail matters more than I have assumed.
Dr.AddMedPHL said:Concentration choice is a precision decision, not a preference.
Right, and one flattering data point from a group buy is not consistency. Consistency means separate batches, separately commissioned, over months.