ANAPHYLAXIS OVERVIEW

Anaphylaxis is a potentially deadly allergic reaction that is rapid in onset. It is most often triggered by foods, medications, and insect stings. There are many other possible triggers.

Anaphylactic reactions are unpredictable. Many people who experience it have a known allergy. Some have had one or more milder allergic reactions previously. Others, who are not even aware that they have an allergy, can suddenly experience severe anaphylaxis. Even the first episode of anaphylaxis can be fatal.

The severity of anaphylactic reactions can be minimized by recognizing the symptoms early, having proper medication available for self-treatment, and seeking emergency medical care promptly. This topic reviews the anaphylaxis treatment and prevention. Separate topics discuss the symptoms and diagnosis of anaphylaxis, and how to use an epinephrine autoinjector. (See "Patient information: Anaphylaxis symptoms and diagnosis (Beyond the Basics)" and "Patient information: Use of an epinephrine autoinjector (Beyond the Basics)".)

ANAPHYLAXIS TREATMENT

A person who has had an anaphylactic reaction should talk with their healthcare professional and develop an Anaphylaxis Emergency Action Plan for responding to future reactions. (See "Anaphylaxis: Rapid recognition and treatment".)

Many people find that having an anaphylaxis treatment plan is reassuring, even if it is never needed. A critical component of the plan is having an epinephrine autoinjector available at all times and knowing when and how to use it. (See 'Self-treatment with epinephrine' below.)

Get emergency help — Because anaphylaxis can be life-threatening, it should be treated as a medical emergency (figure 1). If you are experiencing a sudden allergic reaction that might be anaphylaxis, use your epinephrine autoinjector and then call 911 or emergency medical services (or have someone else call for you). If you are home alone, make sure that the door is unlocked so that the emergency team can enter.

Self-treatment with epinephrine — If you have a history of anaphylaxis, you should always carry at least one epinephrine autoinjector with you at all times. A full description of epinephrine autoinjectors is available separately. (See "Patient information: Use of an epinephrine autoinjector (Beyond the Basics)".)

Epinephrine is the only medicine that completely treats anaphylactic reactions. It is most effective when it is given promptly, before symptoms become severe. Neither antihistamines nor asthma inhalers (puffers) can treat anaphylaxis as effectively as epinephrine, and these medications cannot be substituted for epinephrine.

Remove the cause — The trigger for the anaphylactic reaction should be promptly removed, whenever possible. For example, if you have been stung by a bee and the stinger is still in the skin, flick it out immediately.

Go to the hospital — After injecting epinephrine, it is important to be evaluated in a hospital emergency department. Up to 20 percent of people with anaphylaxis have a late-phase reaction, without further exposure to the trigger, and might require additional anaphylaxis treatment. There is no good way to predict whether a late-phase reaction will occur.

In the emergency department, healthcare providers can monitor you, and if necessary, give oxygen, and insert a breathing tube (endotracheal tube) to keep the airways open until the reaction resolves. When needed, additional doses of epinephrine, intravenous (IV) fluids, and other medications can also be given.

ANAPHYLAXIS PREVENTION

Anaphylaxis is a frightening experience. If you have had one anaphylactic reaction, you are at increased risk for another. It is normal to be anxious about this. The following steps can help to reduce the risk of a future anaphylactic reaction:

See an allergist — Anyone who has experienced an anaphylactic reaction should be evaluated by a doctor with specific training and experience in the diagnosis and treatment of anaphylaxis. Board-certified allergists have such training and experience. (See "Anaphylaxis: Confirming the diagnosis and determining the trigger(s)".)

Testing to determine the trigger — It is important to try to confirm the cause of the anaphylactic reaction. Allergists can perform and interpret skin tests to confirm your specific anaphylaxis triggers (figure 2).

For the most reliable results, skin tests should be performed at least three to four weeks after an anaphylactic reaction, because if done too soon after the event, such tests may give negative results when the person truly does have an allergy. Antihistamines and certain other medications need to be stopped for at least four days before these tests are performed.

Blood tests can be performed immediately after an anaphylactic reaction and medications do not interfere with the results.

In some cases, allergy tests do not identify any specific trigger. This condition is called idiopathic anaphylaxis. It is more common in adults than in children. An allergist can provide the best advice about how to manage this condition.

Avoiding triggers — When a trigger has been identified, you should avoid it. However, avoiding some triggers, such as common foods, can be difficult.

Foods — If you have experienced an anaphylactic reaction due to a food, you should eliminate that food from your diet. This requires that you read and understand food labels and ask about the preparation and content of all foods eaten when away from home. This recommendation applies to everything that you plan to eat, not just the foods that are most likely to contain the trigger. More information about food allergy treatment and prevention is available separately. (See "Patient information: Food allergy symptoms and diagnosis (Beyond the Basics)" and "Patient information: Food allergy treatment and avoidance (Beyond the Basics)".)

An allergist can provide strategies for identifying allergens in processed foods and when dining out. In addition, practical information is available online from the Food Allergy and Anaphylaxis Network (www.foodallergy.org).

Insect stings — People with an allergy to a stinging insect (bees, yellow jackets, wasps, hornets, or fire ants) should wear protective clothing, including closed shoes, and, if allergic to yellow jackets, should avoid drinking from open beverage containers and eating outdoors. (See "Bees, yellow jackets, hornets, and wasps: Avoidance" and "Patient information: Fire ants (Beyond the Basics)".)

A course of allergy shots is recommended for anyone who has had an anaphylactic reaction after an insect sting. The injections are given over several years. They dramatically reduce the person's risk of another episode of anaphylaxis. (See "Hymenoptera venom immunotherapy: Efficacy, indications, and mechanism of action".)

Medications — If you have an allergy to a medication, you should learn all the names of that medication and the settings in which you are likely to encounter it. Ask your healthcare providers to note your allergy in your medical record and on your medical identification device (see below).

Wear medical identification — People who have experienced an anaphylactic reaction should wear a medical identification bracelet or similar medical identification tag at all times. If another reaction occurs and you are too ill to explain your condition, the words "anaphylaxis" or "anaphylactic reaction" will help emergency responders provide prompt and proper care.

The tag should include a list of known allergies, as well as the names and phone numbers of emergency contacts. One device, Medic Alert (www.medicalert.org), provides a toll-free number that emergency medical workers can call to find out a person's medical history, list of medications, emergency contact numbers, and healthcare provider names and numbers.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient information: Anaphylaxis (The Basics)
Patient information: Food allergy (The Basics)
Patient information: Epinephrine auto-injectors (The Basics)
Patient information: Angioedema (The Basics)
Patient information: Insect allergy (The Basics)
Patient information: Peanut allergy (The Basics)
Patient information: Drug allergy (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient information: Anaphylaxis symptoms and diagnosis (Beyond the Basics)
Patient information: Use of an epinephrine autoinjector (Beyond the Basics)
Patient information: Food allergy symptoms and diagnosis (Beyond the Basics)
Patient information: Food allergy treatment and avoidance (Beyond the Basics)
Patient information: Fire ants (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Anaphylaxis: Rapid recognition and treatment
Bee, yellow jacket, wasp, and other Hymenoptera stings: Reaction types and acute management
Clinical manifestations of food allergy: An overview
Diagnosis of Hymenoptera venom allergy
Diagnostic evaluation of food allergy
Differential diagnosis of anaphylaxis in children and adults
Drug eruptions
Fatal anaphylaxis
Food-induced anaphylaxis
History and physical examination in the patient with possible food allergy
Immediate hypersensitivity reactions to radiocontrast media: Clinical manifestations, diagnosis, and treatment
Laboratory tests to support the clinical diagnosis of anaphylaxis
Pathophysiology of anaphylaxis
Anaphylaxis: Confirming the diagnosis and determining the trigger(s)
Bees, yellow jackets, hornets, and wasps: Avoidance
Hymenoptera venom immunotherapy: Efficacy, indications, and mechanism of action

The following organizations also provide reliable health information.

• American Academy of Allergy, Asthma, and Immunology
  
  (www.aaaai.org/patients/gallery/anaphylaxis.asp)
• American College of Allergy, Asthma, and Immunology
  
  (www.acaai.org)
• Anaphylaxis Foundation and Anaphylaxis Network of Canada
  
  (www.anaphylaxis.org)
• The Anaphylaxis Campaign
  
  (www.anaphylaxis.org.uk)
• Food Allergy and Anaphylaxis Network
  
  (www.foodallergy.org/anaphylaxis/index.html)

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