generally (and the exceptions are a bitch) an expired drug is safe but its efficacy is reduced. For some products that rate of reduction is low and an expired product can be good for a year or two after the date (Liquamycin for example), for other products the rate of decline is non linear and fast, so are only good a couple months past date with any real efficacy (Covexin®-8. CDT comes to mind).
Epi seems to be between the two, within some limits:
EpiPen's shelf life has been limited by the chemistry of the drug inside it. Epinephrine is an old and cheap medication, but it's also notoriously finicky. If exposed to light, heat or air, it can degrade, turning rust colored.
The FDA-approved label warns that if the liquid in the pen is discolored, it should be discarded: "Epinephrine solution deteriorates rapidly on exposure to air or light, turning pink from oxidation to adrenochrome and brown from the formation of melanin."
Great! so there's a way to tell, separate from the date!
But what about an expired EpiPen that looks perfectly normal?
The little published data that exists shows that the drug degrades over time -- and color is not an accurate way to gauge whether the epinephrine inside is still good.
well crap, maybe not.
One study, published in the Journal of Allergy and Clinical Immunology in 2000, examined EpiPens one to 90 months after the expiration date. Most were not discolored, but the epinephrine content decreased over time. The study stated that it was best to use EpiPens that had not expired, but found that the pens contained at least two-thirds of the intended dose up to a year after expiration. Even a sub-optimal dose could be better than nothing in a life-or-death situation, the authors concluded.
Looks like if stored in *ideal* conditions the pen will last more than 18 months, but under likely real-world conditions 18 months is it.
FWIW, elsewhere I found that the manufacturer had targeted 27 months, but data only supported 19 months, they went with 18. That's not a large guard band.