Reconstitution arithmetic, done once and written down
Reconstitution arithmetic, done once and written down
Blog Article
The single number that matters after you reconstitute a vial is the concentration, and it is the number people most often fail to write down. Everything else follows from it. If you know how many milligrams sit in each millilitre of the finished solution, every dose question becomes one division. If you do not, you end up re-deriving it under time pressure with a syringe in your hand.
The arithmetic is not hard. Total milligrams in the vial, divided by the millilitres of bacteriostatic water you added, gives milligrams per millilitre. A 5 mg vial reconstituted with 2 mL is 2.5 mg/mL. Reconstitute the same 5 mg with 1 mL and it is 5 mg/mL, and every mark on your syringe now means twice as much. Nothing about the vial changed. Only your own choice of diluent volume did.
That is why the concentration belongs on the vial itself, in marker, the moment you mix it. Not in your head, not in a text message to yourself. On the vial. The person most likely to be confused by an unlabelled vial three weeks from now is you.
The second thing worth recording is the diluent volume you actually added, as distinct from the volume you intended to add. Syringes are not perfectly accurate and people do occasionally add 1.8 mL when aiming for 2 mL. If you write down the real number, your concentration stays honest.
I keep this in a log rather than on paper scraps because the log survives. A Peptide Tracker & Calculator that stores vial strength, diluent volume and the resulting concentration together means the division is done once and then simply read back. It also means the number is still there when a clinician asks what concentration you have been drawing from.
One habit that has saved me more than once: after mixing, work out what your intended dose will be in millilitres and check that it lands somewhere sensible on the syringe. If your dose comes out as 0.06 mL you have chosen too little diluent, because that volume is very hard to measure accurately. Rework the mix before you use it, not after.
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