I would like to call for "experts' opinion"
Pentobarbital sodium (CID: 14075609).
www.ncbi.nlm.nih.gov
This is a rare find: a scientific research study on the longevity and degradation over time of pentobarbital sodium
The conditions of the experiment are typically those of the veterinary liquid format (solution and excipients), commonly stored in a normal fashion (room temperature, away from light), lasting over the span of 6 years
The measurement of the purity deterioration speed is reassuring as very slow, indicating indeed a high stability over time. It potentially backs up, with ease, the calls that a bottle will presumably stay of very high quality after 1, maybe 2 decades
However, it also comments about a colour transformation that occured past the second year mark.
It's unfortunate because the bottle container we're used to, is often brown tainted glass, making it difficult to check without sampling ...and again, a too small volume lacking depth may render the observation awkward.
Unfortunately, it concludes that the coloration alone, despite that the purity almost hasn't changed on the downside, is enough to declare the product improper to use as anaesthetic... why ? What's the explanation to discard a liquid whose active component is still verified as potent ? Is it the right attitude when suspecting a contamination whose nature is unknown ?
I believe this is important to answer because the PPH advises to proceed to a qualitative lab test if a cosmetic change is determined, but also implies that if the lab results return as fine, then it's probably okay to consume
If this experiment is in any way representative, then it makes it a likely event to have to take such a decision after "many years"