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 EpiPen is derived from the Mark I NAAK ComboPen, which was developed for the U.S. military for treating exposure to nerve agents in the course of chemical warfare. Trademark names for the autoinjector device include EpiPen, Emerade, Twinject, Adrenaclick, Anapen, Jext, Allerject, and Auvi-Q.
After activation, the patient holds the device in place for between 5 and 10 seconds as the epinephrine is delivered. This gives the drug enough time to be absorbed by the body's muscles and diffused into the bloodstream.
Auto-injectors are sometimes used unnecessarily. Injection into a vein (intravenous injection) can be fatal. It can cause ventricular tachycardia, in which the heart beats uncontrollably and is not able to pump blood adequately. It can also restrict blood flow to the area of the injection site, and damage the extremities. After administering the device, patients are advised to seek immediate medical attention.
An emergency technique (not manufacturer-approved) to obtain additional epinephrine from a used autoinjector has been published in the medical literature.
Units that have exceeded their expiration date can still be used in an emergency if an unexpired unit is unavailable and the solution is neither discoloured nor contains precipitates.
None of these devices prevent future episodes of anaphylaxis. Patients who experience severe or life-threatening reactions may be treated further via allergen immunotherapy for long-term protection. A series of allergy injections composed of increasing concentrations of naturally occurring substances (such as venom) provide excellent and usually lifelong protections against adverse effects of future insect stings. The initial injections have a very low concentration, usually 1 ppb or less.
The devices contain a spring-loaded needle that exits the tip of the device (in some cases through a sterile membrane) and penetrates the recipient's skin, to deliver the medication via intramuscular injection.
Epinephrine autoinjectors contain a pre-determined dose of epinephrine, usually between 300 μg and 500 μg of active ingredient at a concentration of 1:1000. They typically contain more medication than the amount needed for a single dose, but any extra amount is not intended for use and is inaccessible without destroying the device. Manufacturers have also made pediatric dosed versions available at 150 μg of active ingredient. There was a version that contained two individual doses (in case a repeated application is required) previously sold under the trade name Twinject. The company that produced Twinject autoinjectors, Shionogi, announced that it was discontinuing Twinject effective March 30, 2012.
On August 13, 2012, the U.S. Food and Drug Administration (FDA) approved a new version of epinephrine auto-injector developed by Intelliject equipped with a sound chip to provide electronic voice instructions  to guide the user in the proper use of the device. (The device is made and marketed by Sanofi who licensed the North American commercialization rights to it from Richmond-based kaléo, formerly known as Intelliject.) It is called Auvi-Q in the US (the same name initially used by Intelliject), and Allerject in Canada. The device is rectangular in shape, 3.5 inches by 2 inches by 0.5 inch.
In nearly all countries, epinephrine is a prescription drug, and therefore obtaining the device requires a prescription from a doctor. However, according to some published reports, epinephrine autoinjectors are an over-the-counter drug in some countries, but credible information as to the specific countries is not available.[where? ]
The epinephrine auto-injection devices made by drugmaker Sanofi, sold in the US as Auvi-Q and in Canada as Allerject, were voluntarily recalled on October 28, 2015. The reason stated by Sanofi was that the products have been found to potentially have inaccurate dosage delivery, which may include failure to deliver drug. 
In its news Release on October 28, 2015, Sanofi Canada stated that it was "actively working with suppliers of alternative epinephrine auto-injectors to have a full stock available in Canada as soon as possible. Canadian customers were asked to immediately return the product to their local pharmacy to obtain an alternate epinephrine auto-injector." The Canadian Medical Association Journal on November 3, 2015 indicated that availability of the most popular alternative product would be great within a few days because Pfizer Canada confirmed that it had shipped its entire inventory of EpiPen products to wholesalers, and has ordered five times its usual stock of EpiPen and EpiPen Jr to meet the unexpected demand."
The U.S. Food and Drug Administration confirmed the recall of all current Auvi-Q products  on its web site and provided information for affected consumers in the United States. Sanofi US confirmed on its web site that it will provide reimbursement for out of pocket costs incurred for the purchase of new, alternate epinephrine auto-injectors to replace Auvi-Q, with proof of purchase. The manufacturer of the most popular autoinjector products, Mylan, indicated after the Sanofi recall that it would have a sufficient supply of EpiPens to meet any anticipated demand.
- Smetana, Kevin (September 24, 2009). "EpiPen inventor helped millions and died in obscurity". St. Petersburg Times. Retrieved 2010-07-07.
- Hawkins, S (December 2013). "Retrieval of Additional Epinephrine from Auto-Injectors". Wilderness & Environmental Medicine 24: 434–444. doi:10.1016/j.wem.2013.03.025.
- Simons, FE; Gu, X; Simons, KJ (May 2000). "Outdated EpiPen and EpiPen Jr autoinjectors: past their prime?". The Journal of allergy and clinical immunology 105 (5): 1025–30. doi:10.1067/mai.2000.106042. PMID 10808186.
- Resiman, R (August 1994). "Insect Stings". New England Journal of Medicine 26: 523–7. doi:10.1056/NEJM199408253310808. PMID 8041420.
- "Epipen and Epipen Jr; Dosing | Epinephrine Dose | Anaphylaxis". EpiPen. Retrieved 2010-07-07.
- "Anapen 300 product information sheet". Lincoln Medical Ltd.
- "Anapen 500 product information sheet". Lincoln Medical Ltd.
- "Anapen 150 product information sheet". Lincoln Medical Ltd.
- Verus Pharmaceuticals Announces U.S. Launch of Twinject for Anaphylaxis
- "ALK media release (07 October 2010)". Retrieved 2014-04-08.
- "ALK media release (13 October 2010)". Retrieved 2014-04-08.
- "ALK media release (06 September 2011)". Retrieved 2014-04-08.
- "Auvi-Q Fact Sheet" (PDF). Retrieved 18 August 2012.
- http://www.allerject.ca/en/epinephrine-autoinjector Allerject
- BMJ Clinical Review of Epinephrine Administration. Accessed on March 19, 2007.