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Diclofenac patches often, maybe always, have an expiration date. How does the efficiency of a diclofenac patch decrease as it approaches the expiration date?

Assume that the diclofenac patch is used to treat a lateral epicondylitis of the humerus, and that storage instructions were properly folowed (e.g., "Store patches in the envelope at room temperature at 77 degrees F (25 degrees C). Brief storage between 59-86 degrees F (15-30 degrees C) is permitted. Always reseal envelope after opening").

Some websites claim diclofenac patches are useless after the expiration date:

https://umm.edu/health/medical/drug-notes/notes/diclofenac-patch-on-the-skin :

You will also need to throw away old patches after the expiration date has passed.

But it doesn't tell me to what extent the efficiency of a diclofenac patch decreases as it approaches the expiration date.

Butterfly and Bones
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Franck Dernoncourt
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  • Drug shelf-life is there to ensure up to 90 % efficacy. What happens next can only be answered by the person running the QC tests at the manufacturing company, and whoever sees those results. In the case of some drugs, the products resulting from loss of quality can be outright dangerous, but in most cases, the problem is you can't know how much drug was administered (does it have 60% remaining after a month, 80, 40, what?), and thus the doctor cannot make decisions about the therapy (Add drugs? Switch to oral diclofenac? Switch drug? Continue as usual?). – M.A.R. Apr 30 '23 at 18:19

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