Epinephrine autoinjector

An epinephrine autoinjector is a medical device for injecting a measured dose or doses of epinephrine (adrenaline) by means of autoinjector technology. It is most often used for the treatment of anaphylaxis. The first epinephrine autoinjector was brought to market in the 1980s.

Epinephrine autoinjectors are hand-held devices carried by those who have severe allergies; the epinephrine delivered by the device is an emergency treatment for anaphylactic reaction.

When anaphylaxis is suspected, epinephrine solution should be injected into the thigh muscle as soon as possible. The injection may be repeated every 5 to 15 minutes if there is insufficient response. A second dose is needed in 16–35% of episodes with more than two doses rarely required; in around 80% of the cases where a second dose is administered, it is by a medical professional. It is not clear which are the people who might need a second injection at the outset. The intramuscular route is preferred over subcutaneous administration because the latter may have delayed absorption. Minor adverse effects from epinephrine include tremors, anxiety, headaches, and palpitations.

The epinephrine in autoinjectors expires after one year. A study in rabbits showed that intramuscular epinephrine works less well after it expires; that study also recommended that if the drug in an expired device has not started to precipitate (if the solution is not cloudy and has no particles in it) using the expired device is better than no injection at all in an emergency situation.

The devices contain a fixed dose of epinephrine and a spring-loaded needle that exits the tip or edge of the device and penetrates the recipient's skin, to deliver the medication via intramuscular injection.

People to whom epinephrine autoinjectors are prescribed need to be trained how to use the specific device prescribed. The rate of unintentional injections using these devices is unknown but a 2009 review found that the rate is increasing. Unintentional injections are delivered to a finger or thumb around 90% of the time; they cause intense pain locally but usually completely resolve. The cause of unintentional injections has been attributed to design flaws, where the device is mistaken for a pen or the user mistakes which end of the device contains the needle.

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