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Johns Hopkins Symptoms and Remedies

Johns Hopkins Medicine

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Anaphylaxis

What is it?

Anaphylaxis is a severe, life-threatening allergic reaction that affects organ systems throughout the body. It occurs when the immune system becomes sensitized to an allergen, such as a food, drug, or insect venom. Upon reexposure to the allergen, the immune system overreacts, releasing cascades of histamine and other substances that can cause contraction of the intestinal smooth muscles, skin reactions, constriction of the airways, and a precipitous drop in blood pressure that may lead to shock. Immediate medical attention is essential; severe cases may prove fatal even with treatment.

What Causes It?

  • An insect sting.
  • Ingestion of a food or food additive. Peanuts are the most common cause of food-induced anaphylaxis.
  • Injection of a drug, vaccine, or a chemical used in a diagnostic procedure. Penicillin is the most common cause of drug-induced anaphylaxis. Some oral drugs can also trigger the reaction.
  • Rarely, symptoms occur without apparent exposure to a known cause.

Prevention

  • Avoid allergens that have caused an adverse reaction in the past.
  • People who have previously had a severe allergic reaction should wear a Medic-Alert bracelet and get a prescription for epinephrine (adrenaline), which halts the allergic reaction and should be carried at all times. An easy-to-use form is the Epi-pen, a spring loaded device that automatically injects a dose of epinephrine when pressed against the skin (usually the leg). The drug does not substitute for necessary medical treatment but does buy valuable time until help can be found.

Diagnosis

  • Diagnosis is indicated by the sudden onset of characteristic symptoms, usually within five minutes to one hour following exposure to a suspected allergen. Since anaphylaxis is an emergency, immediate treatment supersedes the need for further confirmatory procedures. Tests for the specific allergen may be done after the patient has stabilized.

How to Treat It

  • Immediate medical treatment is necessary. An injection of the adrenal hormone epinephrine (adrenaline) is necessary to counteract the effect of histamine throughout the body. Doses may need to be repeated every 10 to 20 minutes until the reaction ceases.
  • Inhalers such as albuterol improve breathing.
  • If life-threatening breathing obstruction has occurred due to swelling of the larynx, a tube may be placed through the mouth or nose to aid in breathing; in very serious cases a tracheostomy (insertion of a breathing tube through a surgical opening in the throat) may be needed.
  • Intravenous fluids containing blood pressure-raising agents are administered if shock occurs.
  • Antihistamines (such as diphenhydramine) or corticosteroids (such as prednisone) may be used after the initial crisis has passed to prevent return of symptoms.

When to Call a Doctor

  • EMERGENCY An anaphylactic reaction requires immediate medical attention. Call an ambulance or get to an emergency room right away.