The potency of epinephrine in autoinjector (EpiPen) may deteriorate after the expiration date. This is because it is an unstable chemical in aqueous solution.
Deterioration may occur on exposure to air or light to:
(1) adrenochrome (pink)
(2) brown (melanin)
Deterioration may also occur if the pen is refrigerated or exposed to heat.
The line in Figure 2 plotting months vs percent of labeled potency can be approximated by the line:
estimated percent of labeled potency from 0 to 60 months after expiration =
= 95.48 - (0.4245 * (months after expiration))
If an outdated autoinjector is the only source of epinephrine available for a patient undergoing an anaphylactic reaction, then it still can be used (since it is better than nothing) unless a visual inspection shows:
(1) discoloration
(2) precipitates
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