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Who needs to carry an epinephrine autoinjector?

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ABSTRACT

Patients who have had anaphylaxis or who are at risk of it (eg, due to food allergy or Hymenoptera hypersensitivity) should carry an epinephrine autoinjector at all times. However, the risks and benefits must be considered on an individual basis, especially in patients with atherosclerotic heart disease, elderly patients on polypharmacy, patients receiving allergen immunotherapy, those with large local reactions to insect stings, and individuals with oral allergy syndrome.

KEY POINTS

  • Based on current data, there is no absolute contraindication to epinephrine for anaphylaxis. And failure to give epinephrine promptly has resulted in deaths.
  • Clinicians concerned about adverse effects of epinephrine may be reluctant to give it during anaphylaxis.
  • Education about anaphylaxis and its prompt treatment with epinephrine is critical for patients and their caregivers.


 

References

Anaphylaxis is potentially fatal but can be prevented if the trigger is identified and avoided, and death can be avoided if episodes are treated promptly.

A consensus definition of anaphylaxis has been difficult to achieve, with slight variations among international guidelines. The World Allergy Organization classifies anaphylaxis as immunologic, nonimmunologic, or idiopathic.1 The National Institute of Allergy and Infectious Diseases and the Food Allergy and Anaphylaxis Network highlight clinical symptoms and criteria.2 The International Consensus on Food Allergy describes reactions as being immunoglobulin E (IgE)-mediated, cell-mediated, or a combination of the 2 mechanisms.3

Despite the subtle differences in these definitions, all 3 international organizations have a common recommendation for anaphylaxis: once it is diagnosed, epinephrine is the treatment of choice.

EPINEPHRINE IS THE TREATMENT OF CHOICE FOR ANAPHYLAXIS

Anaphylaxis commonly results from exposure to foods, medications, and Hymenoptera venom.4 Avoiding triggers is key in preventing anaphylaxis but is not always possible.

Although epinephrine is the cornerstone of the emergency treatment of anaphylaxis, many patients instead receive antihistamines and corticosteroids as initial therapy. Some take these medications on their own, and some receive them in emergency departments and outpatient clinics.5

Diphenhydramine, a histamine 1 receptor antagonist, is often used as a first-line medication. But diphenhydramine has a slow onset of action, taking 80 minutes after an oral dose to suppress a histamine-induced cutaneous flare by 50%, and taking 52 minutes with intramuscular administration.6 Corticosteroids also have a slow onset of action. These drugs cannot prevent death in anaphylaxis, a condition in which the median time to respiratory or cardiac arrest is 30 minutes after ingestion of food, 15 minutes after envenomation, and 5 minutes after iatrogenic reactions.7

Combination therapy with diphenhydra­mine and a histamine 2 receptor antagonist (eg, cimetidine, famotidine) is also commonly used,8 but this combination offers no advantage in terms of onset of action, and a Cochrane review could find no definitive evidence for or against the use of histamine 2 receptor antagonists.9

Because of their slow onset of action, all of these should be second-line therapies, given after epinephrine. Epinephrine is the first line of treatment because it has a maximal pharmacokinetic effect (time to maximal peak serum level) within 10 minutes of intramuscular injection into the thigh.10,11

In addition, epinephrine acts on numerous receptors to antagonize the multiple pathologic effects of the mediators released during an anaphylactic episode. In contrast, antihistamines block only 1 mediator, while mediators other than histamine can be responsible for severe events and deaths.12,13

It is crucial that epinephrine be given immediately, as delay has been associated with fatalities.14 In addition, guidelines recommend repeating epinephrine dosing after 5 to 15 minutes if the response to the first dose is suboptimal.1,2 From 16% to 36% of patients may need a second dose.15–18 Therefore, many physicians recommend that patients at risk of anaphylaxis keep not 1 but 2 epinephrine autoinjectors on hand at all times, and so say the US guidelines for the management of anaphylaxis.19

WHO SHOULD CARRY AN EPINEPHRINE AUTOINJECTOR?

All published guidelines recommend epinephrine as the drug of choice for anaphylaxis. And an epinephrine autoinjector is indicated for anyone who has experienced an anaphylactic event or is at risk of one, and these patients should carry it with them at all times. Such individuals include those with food allergy or Hymenoptera hypersensitivity.

Food allergy

The foods that most often cause anaphylaxis are peanuts, tree nuts, fish, shellfish, milk, and eggs, but any food can cause a reaction.

The prevalence of food allergy has increased over time, and treatments are limited. Some food desensitization protocols look promising but are still in the research stages. The best treatment at this time is to avoid the offending food, but there are accidental exposures.

Hymenoptera hypersensitivity

Patients who have had anaphylaxis after being stung by insects such as bees, wasps, yellow-faced hornets, white-faced hornets, yellow jackets, and fire ants should be evaluated by an allergist. Skin testing and serum IgE testing helps properly diagnose Hymenoptera hypersensitivity.

Once the diagnosis is confirmed, venom immunotherapy should be considered. Some patients choose only to carry an epinephrine autoinjector and to avoid these insects as much as possible. However, most patients also choose to receive venom immunotherapy, because 80% to 90% of those who receive this treatment for 3 to 5 years do not have a systemic reaction if they are stung again.20

Regardless of whether they choose to undergo immunotherapy, sensitive patients should always carry an epinephrine autoinjector. This is also the case after treatment ends, since the therapy is not 100% effective.

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