Assuming the following conditions, what are the primary mechanisms of breakdown?
- Dry powder form (not in any pill or packaging)
- Stored in a glass bottle
- Not exposed to light
- 22C ambient temperature
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$\begingroup$ For a start, I suggest to look into the documentation that comes with the medication. What does it say? Of course the active ingredient may degrade, but also other parts of the formulation. Intact packaging is obviously important. $\endgroup$– SnijderfreyJan 4 at 0:16
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1$\begingroup$ Each is different, and even different manufacturers of the same formulation could have differing storage recommendations. The best you can do is research each online, e.g., medlineplus.gov/druginfo/meds/a685001.html#storage-conditions , and look for commonalities. $\endgroup$– DrMoishe PippikJan 4 at 1:46
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1$\begingroup$ For compounds, there is universal advice of low T, darkness and low humidity, with need of proper temperation in both ways. ( To prevent high or condensing package humidity when cooled down too fast even with desiccant. And similarly condensing external humidity at shocking warm up.) // Particular advises are highly specific. $\endgroup$– PoutnikJan 4 at 9:58
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1$\begingroup$ One can't generalize about conditions. For example, low temperatures may cause a medication delivered as an emulsion to separate through freezing, or crack the shell of a capsule as contents expand, contract or crystallize. $\endgroup$– DrMoishe PippikJan 4 at 14:44
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1$\begingroup$ This gives some ideas what happens in the presence of water and oxygen: sciencedirect.com/science/article/abs/pii/S0045653513002245 $\endgroup$– Karsten ♦Jan 14 at 16:14
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1 Answer
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Karsten's reference to Gozlan et al., Chemosphere (2013) 91(7), 985-992 appears to show that the major breakdown route under the reported wet conditions was to open the beta-lactam ring hydrolytically to form the corresponding penicilloic acid.
In any other conditions, the strained 4-membered beta-lactam ring seems on many reckonings still likely to be the most reactive (~unstable) part of the molecule, together with its fused thiazolidine ring partner.
Under the storage conditions mentioned in the question (i.e. 'dry' but in an unspecified hence presumably ordinary bottle), there may be a shortage of water but probably not a complete absence. So it might be expected that some hydrolytic decomposition to the penicilloic acid would happen unless the 'dry' character has been taken even further by freeze-drying and storage in sealed ampoules.
Under freeze-dried conditions, there might still be residual room for slower ring-opening reactions between amoxicillin molecules.
