Adrenaline (epinephrine) is the first-line treatment for anaphylaxis, and two types of adrenaline injector are available for use in Australia. Prescribers need to be aware of the different instructions for their use and recent changes to adrenaline dose recommendations.
Anaphylaxis is a severe, potentially life-threatening allergic reaction, and intramuscular (IM) adrenaline (epinephrine) is the treatment of choice.1-4 Adrenaline injectors (AI) have been available for more than 40 years and allow rapid administration of IM adrenaline by the patient or a lay person.5-7 In Australia, the EpiPen AI has been available on the PBS since 2003. From 2021, a second type of AI device that can deliver a higher dose is also available on the PBS, Anapen. Here, we discuss the role of AIs in treating anaphylaxis, how to prescribe them, including dose and patient education, and compare EpiPen and Anapen.
What are adrenaline injector devices?
AIs are single-use devices that deliver a set dose of adrenaline, designed for use by people without medical training to treat anaphylaxis. Adrenaline is the only first-line drug to treat anaphylaxis and should be administered promptly by IM injection into the outer mid-thigh.1-3 IM administration has been the route of choice for optimal delivery of adrenaline in treating anaphylaxis for over 20 years.1,3,4,8 There are no contraindications to the use of IM adrenaline to treat anaphylaxis.2,4
Adrenaline is a nonselective adrenergic agonist with a rapid onset of action. Adrenaline acts to reduce airway mucosal oedema, induce bronchodilation, induce vasoconstriction and increase cardiac contraction strength.1,4 Two AI devices are TGA approved and available in Australia, with both listed on the PBS: Anapen (containing 150, 300 or 500 mcg doses) and EpiPen (containing 150 or 300 mcg doses). A generic AI similar to EpiPen is also PBS listed. AIs are designed to keep adrenaline stable and have an expiry date in excess of one year after manufacture.
When to use an AI device
AIs are used for the first-line treatment of anaphylaxis. Anaphylaxis is a severe allergic reaction that is often under-recognised and undertreated.1,3,9 Definitions vary worldwide, but the Australasian Society of Clinical Immunology and Allergy (ASCIA) defines anaphylaxis as:2
- any acute onset illness with typical skin features (urticarial rash or erythema/flushing, and/or angioedema), plus involvement of respiratory and/or cardiovascular and/or persistent severe gastrointestinal symptoms (gastrointestinal symptoms of any severity are a symptom of anaphylaxis to insect stings or injected drugs); or
- any acute onset of hypotension or bronchospasm or upper airway obstruction where anaphylaxis is considered possible, even if typical skin features are not present.
The ASCIA definition is consistent with the criteria published in the World Allergy Organization (WAO) Anaphylaxis Guidance 2020.3
AIs may be self-administered or given by people without medical training. AIs are also sometimes used to treat anaphylaxis in medical facilities as they contain a fixed dose of adrenaline, which may reduce the risk of overdose and delays in administration.