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- 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
- 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.
- Previous anaphylaxis
- History of atopy or asthma
Genetic predisposition for sensitization to antigens
- 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.
- 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)
- Foods (commonly, peanuts, nuts, fish, crustaceans, mollusks, cow’s milk, eggs, and soy)
- Insect stings (e.g., honeybees, wasps, kissing bugs, and deer flies)
- Latex rubber (gloves, catheters)
- Macromolecules (e.g., chymopapain, insulin, dextran, glucocorticoid, and protamine)
Commonly Associated Conditions