How many times can a rubber stopper realistically be pierced?

I have photographs before and after reconstitution if the visual detail matters.

This is a procedural question rather than a theoretical one, and I would like the procedure rather than the theory.

What I have done so far is read the label documentation where it exists and the two pharmacopoeial monographs that are publicly available, which cover the licensed presentation and say nothing about a research one.

What would you do, and what would you check afterwards?

The answer depends on exactly which dose and which vial you are asking about, but the method is always the same.

The rounding error accumulates if you round too many times — rounding concentration to 5.0, rounding the dose volume to 0.1 mL, rounding the unit reading to 10 — and the safest approach is to work the full precision and round only the final answer.

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.

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

edited 22 Jul 2025 by fib4_reader — added a caveat about sampling

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

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.

Specifically, the concentration you actually work with is label claim times content fraction divided by actual diluent volume, which is usually not the same as the nominal concentration because content is usually not 100 per cent and you rarely measure the diluent volume to 0.1 mL precision.

The Arrhenius relationship for drawing kinetics means that cold solution takes noticeably longer to draw than room-temperature solution.

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

Work in the order concentration, then volume, then units, and the arithmetic stops being confusing. Concentration is milligrams per millilitre and comes from the vial contents and the diluent volume. Volume per dose is dose divided by concentration. Units on a U-100 syringe are volume in millilitres multiplied by one hundred.

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.

Write the units at every step, because units errors are the failure mode that catches everyone eventually.

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.

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