Description

• An IgE-mediated, acute systemic reaction following antigen exposure in a sensitized person
• A non–IgE-mediated idiopathic anaphylactoid reaction also may occur. Anaphylactoid reactions are clinically indistinguishable from anaphylaxis and are treated in the same manner.
• System(s) affected: Cardiovascular; Endocrine/Metabolic; Gastrointestinal; Hematologic/Lymphatic/Immunologic; Pulmonary; and Skin/Exocrine
• Synonym(s): Anaphylactoid reactions

Epidemiology

• Predominant age: All ages
• Predominant sex: Male = Female

• Up to 40,000 cases of idiopathic anaphylaxis with no identifiable cause occur each year.
• Drug-induced anaphylaxis occurs in 1/2,700 hospitalized patients.
• Anaphylaxis deaths: 0.3–0.7/100,000 per year
• Food allergic reactions constitute 1/3–1/2 of all anaphylactic reactions worldwide.
• Anaphylaxis may occur secondary to allergy skin testing.
• Asthmatics are more prone to anaphylaxis than nonasthmatics. Female asthmatics are at greater risk of anaphylaxis than their male counterparts.

Risk Factors

• Previous anaphylaxis
• History of atopy or asthma

Genetics
Genetic predisposition for sensitization to antigens

General Prevention

• Avoid inducing drugs and foods.
• For those with history of anaphylaxis, carry a prefilled epinephrine syringe. Keep a syringe at home, work/school, and in vehicle, although syringe should be protected from temperature extremes.
• Avoid areas where insect exposure is likely. Avoid wearing insect attractants (e.g., perfumes, colored clothing); avoid bare feet outdoors.
• Carry or wear a medical alert ID about the anaphylaxis-causing substance or event.
• When radiologic contrast is unavoidable, use of low-osmolar contrast agents (e.g., iothalamate) reduces the risk of contrast reactions to 3.1%:
  • Only 0.22% were considered severe.
  • Stop beta-blockers before administering contrast materials.
  • Pretreat with diphenhydramine (50 mg IV) and a steroid (e.g., methylprednisolone 60 mg IV q6h) until procedure. Start methylprednisolone the day before the procedure is scheduled.
  • Those with frequent (>6 per year) episodes of idiopathic anaphylaxis should be treated prophylactically with prednisone (40–60 mg/d in a single morning dose), hydroxyzine (25 mg t.i.d.), and albuterol (2 mg PO t.i.d.). The prednisone should be rapidly tapered to an every-other-day regimen.

• Have a latex-free kit (gloves, etc.) available for the treatment of latex-allergic patients. Some latex-allergic patients will react to tropical fruits, such as kiwi, bananas, avocados, and chestnuts.
• Avoid beta-blockers.

Etiology

• IgE-mediated mast cell degranulation
• Complement activation (C3a, C4a, C5a) by antigen–antibody complexes that contain complement-fixing antibodies
• Other non–IgE-dependent anaphylaxislike syndromes may be caused by modulators of arachidonic acid metabolism, sulfiting agents, exercise-induced anaphylaxis, and idiopathic recurrent anaphylaxis.
• Some important causes of anaphylaxis are:
  • Antimicrobials (e.g., penicillin)
  • Blood products (especially in IgA deficiency)
  • Iodinated contrast media
  • Ethylene oxide gas (dialysis tubing, other sterilized products)
  • Exercise
  • Foods (commonly, peanuts, nuts, fish, crustaceans, mollusks, cow’s milk, eggs, and soy)
  • Immunotherapy
  • Insect stings (e.g., honeybees, wasps, kissing bugs, and deer flies)
  • Latex rubber (gloves, catheters)
  • Macromolecules (e.g., chymopapain, insulin, dextran, glucocorticoid, and protamine)
  • Vaccines

Commonly Associated Conditions

• Asthma
• Atopy