u/rosa_mensah

reconstituting at a round concentration makes every later dose easy

How many mg in the vial and how many mL are you adding?

write the concentration on the vial in marker, that is the whole post

Adding more water does not change how much peptide is in the vial.

Right, and the arithmetic behind it: 15mg in 3mL is 5mg/mL, so 5mg is 100 units.

twice as much water halves the concentration and doubles the units for the same dose

aim the stream at the glass wall, not at the cake

I would not round that figure. At 1.67mg/mL a rounding error of two units is a real fraction of the intended amount.

What concentration did you actually reconstitute at, rather than what did you intend to?

twice as much water halves the concentration and doubles the units for the same dose

Show the arithmetic — where did the unit figure come from?

Agreed — units are volume. Once that lands, the rest of the arithmetic is one division.

I keep a laminated card in the drawer with the arithmetic on it. Looks ridiculous. Has never once let me draw the wrong volume.

If your calculation produces a fraction of a unit, the concentration is wrong for your dose. Change the water volume until the numbers land on whole units.

Bacteriostatic water contains benzyl alcohol as a preservative, which is what makes repeated entry into the same vial reasonable. Plain sterile water has no preservative.

Disagree with the "more water is safer" framing. It is not safer, it is just a different number to divide by.

How many mg in the vial and how many mL are you adding?

Adding one thing — put the date on the label too. Concentration plus date and you can never mix two vials up.

Small fix — a U-100 syringe is 100 units per mL. If yours is marked differently it is not U-100 and the whole calculation changes.

Wrote the date on the vial as well as the concentration after losing track of which one was opened first.

This. Showing the working is the fastest way for somebody else to spot the mistake.

Bacteriostatic water contains benzyl alcohol as a preservative, which is what makes repeated entry into the same vial reasonable. Plain sterile water has no preservative.

Started reconstituting everything to a round concentration and the six-in-the-morning error rate went to zero.

Correction: that gives 5 units, not what you have written. 30mg into 3mL is 10mg/mL and the division follows from there.

more water is not more drug, it is the same drug in a bigger volume

Cosigning the round-number approach. Reconstituting to something awkward is how you end up drawing 27.5 units at six in the morning.

Reconstituted at 1mL when I meant to use a different volume. Caught it because the units looked wrong on the barrel. Now I write 5mg/mL on the glass before I put the cap back.

This. Showing the working is the fastest way for somebody else to spot the mistake.

That only works if the fill weight is exactly the label weight, and it usually is not exactly anything.

aim the stream at the glass wall, not at the cake

Spent 10 weeks confused about this until somebody drew the table for me. 20mg, 3mL, 6.67mg/mL, 5mg is 75 units. That is the whole thing.

The dead space question sent me down a rabbit hole for a week. It is a fraction of a unit and it is the same every draw.

Agreed on the swirl. There is no reason to shake it and a good reason not to.

reconstituting at a round concentration makes every later dose easy