Second pass at: A reconstituted vial's beyond-use date and the reasoning behind common figures

Second pass at: A reconstituted vial's beyond-use date and the reasoning behind common figures Writing it up because I had to work it out twice and would rather nobody else did.

Something changed and I would like to know whether it should have.

Same compound, same supplier, same technique, 3 weeks apart, and the experience is not the same. I have ruled out the obvious differences and I am left with the ones I cannot rule out from here.

Before anyone suggests it: yes, I have the dates written down, and yes, I checked them rather than remembering them.

Fine by me. I had wanted a stronger conclusion and there is not one available.

Adding the measurement that the opening post says would settle it.

A beyond-use date on a home preparation is an inference rather than a measurement. It can be a reasonable inference and it should be described as one.

Anyone with a larger sample, please post it.

Where I part company with the opening post, and it is a narrow parting.

Vial integrity: once a vial is entered with a needle repeatedly, the rubber closure degrades and the integrity fails. Using the same vial repeatedly over weeks or months carries increasing risk of contamination. Single-use vials entered once are lowest risk.

One case, stated as one case.

Beyond-use dating: the date after which a prepared solution should not be used. It is an estimate based on how fast the solution degrades under stated storage, not on whether the solution suddenly becomes unusable on a calendar date. The date is a boundary; crossing it is a risk factor not a certainty of damage.

I keep a log of this specifically because memory is unreliable about it.

Temperature excursions: if a vial sat at room temperature for a time, the question is whether the excursion was long enough to cause damage. Hours at room temperature is usually low risk. Days to weeks raises the risk. If you are unsure, contacting the supplier is more informative than guessing.

Published stability data applies specifically to the formulation studied, under the specific conditions stated. It does not automatically transfer to something reconstituted at home in a different concentration with a different diluent. That caveat is not small.

Stating my assumptions rather than smuggling them in.

I read post #5 twice before replying, because I had assumed the opposite.

Light protection is easy and cheap. The original carton exists for a reason and a vial stored in it is protected without anybody having to think about it again.