Reconstitution & syringe-unit calculator

The three mistakes

One. Confusing units with millilitres. On a U-100 syringe one unit is 0.01ml, so 100 units is 1ml and 25 units is 0.25ml. The syringe is marked in units because it was designed for insulin, and the marking has nothing to do with milligrams of anything.

Two. Choosing a diluent volume before choosing the dose. Pick the volume so the dose you actually intend to draw lands on a round number of units. 10mg in 2ml gives 5mg/ml, so 0.5mg is exactly 10 units. 10mg in 2.5ml gives 4mg/ml, and the same 0.5mg becomes 12.5 units — a half-unit mark you will misread at seven in the morning for the next eight weeks. The table above exists to make that choice for you.

Three. Over-diluting to make the number look nicer. Beyond a point the measurement error on a very small volume is worse than the inconvenience of a slightly awkward one. If your dose is under about 5 units on a U-100, use less diluent.

Bacteriostatic versus sterile water

Bacteriostatic water contains roughly 0.9% benzyl alcohol as a preservative. Sterile water contains nothing. For any vial you intend to enter more than once, the room's settled position is bacteriostatic water. For a single-entry vial either works, though several members find bacteriostatic stings less going in — which is not the reason it exists.

Technique, in the order it matters

1. Let the vial and the diluent come to room temperature. Cold stings and nothing else.
2. Swab both stoppers and let the alcohol dry. This is the single largest cause of injections that hurt.
3. Draw the diluent, insert into the lyophilised vial, and let the vacuum pull it in. Aim the stream at the glass wall rather than at the powder.
4. Swirl. Do not shake. Foam is denatured protein and you are not getting it back.
5. Wait until it is completely clear with no visible particles. A few minutes is normal. Cloudy is not.
6. Write the concentration and the date on the vial in marker. Every member who has skipped this has regretted it.