What would make you reject a TFC vial on visual inspection alone?

My setup is a refrigerator with a logger and a small work area I wipe down, nothing more.

I want to decide this in advance so that I am not deciding it under pressure later.

Assume I will follow the plan I write down, so I would like it to be a good one.

What should I decide now, and what should I defer?

Dose arithmetic has three parts: concentration from vial content and diluent, volume from dose and concentration, and units from volume and syringe scale.

On filtration: a 0.22 µm syringe filter will remove particulates and organisms, and it will also adsorb a fraction of your peptide onto the membrane — with a low-binding PVDF or PES membrane the loss is typically a few per cent.

To be exact about it, rotation of injection site is a tolerability measure, not a pharmacokinetic one, but if you are going to do it you might as well do it right.

The insulin-unit standard U-100 means 100 units per millilitre, so one unit is 0.01 mL — this is the conversion that trips up more people here than any other single piece of arithmetic.

Write the arithmetic on the vial label. It costs nothing and removes the step where you reconstruct it from memory.

The distinction that resolves most of these questions is understanding what concentration actually means and why it is not the same as label claim.

Do not use the same needle to pierce the stopper and to administer. The tip is blunted by the stopper, and the hub now contains a dose you are about to lose to dead space anyway.

Air bubbles at these volumes are a measurement problem rather than a safety one. A 2 mm bubble in a 0.3 mL syringe is roughly 4 µL, which at 10 units drawn is a four per cent error.

Do the arithmetic twice, ideally with someone else doing it independently.

Put another way, two people working through the same arithmetic independently should get the same answer, and if they do not, someone has made a unit error.

Number of stopper piercings matters less than the gauge doing the piercing. A 30G or 31G needle through a butyl stopper leaves a track that reseals; a 21G or 18G drawing needle punches a core and can drop it into the solution.

The content assay results from major testing services show that nominal vial claim and measured content differ by one to ten per cent, making content a driver of dose error.

One qualification: if your arithmetic and someone else's disagree by a factor of ten, one of you has made a unit error, and writing out the units at every step is the diagnostic.

If in doubt, use more diluent and accept the shorter usable window.

edited 26 Nov 2025 by vialroom — fixed an arithmetic slip in the third paragraph

On the detail: the arithmetic only stops being confusing once you work it through once and see that it is straightforward.

Room temperature before drawing is worth the ten minutes. Cold solution is more viscous, draws slower, and condensation on a cold barrel makes it harder to read the meniscus.

Worth noting: the concentration after reconstitution is not the same as the label claim, and most people do not account for the difference.

Write the arithmetic on the vial label. It costs nothing and removes the step where you reconstruct it from memory.