Vial has gone slightly cloudy. Is that always the end of it?

Reconstituted vial, a couple of weeks in the fridge, now faintly hazy rather than clear. Nothing visible floating.

Is haze always bad or can it be something benign?

Cloudiness can be several things and none of the benign ones are worth the risk of guessing wrong.

Benign-ish possibilities: undissolved material that never fully went in; something coming out of solution as it cooled; occasionally an excipient behaving oddly.

Not benign: aggregation, which is peptide molecules clumping and is both a loss of the material and an immunogenicity concern. Or microbial growth, which is the one that matters immediately.

The problem is that you cannot distinguish them by looking. There is no visual test that separates aggregate from growth.

From a purely practical standpoint the answer is not complicated. A parenteral solution that is not clear when it should be clear does not go in a person. That is the rule everywhere it is anybody's job to have a rule about it.

The value of a vial is never the deciding factor in that comparison.

Fair. I was hoping for a way to tell and there is not one.

The absence of a way to tell is the answer. If it were distinguishable there would be a test and somebody would sell it.

Also worth asking what changed. Two weeks in a fridge door is a different two weeks from two weeks at the back of the shelf.