Anaphylaxis and Anaphylactoid Reactions: Diagnosis and Management

Anaphylaxis is an acute fatal or potentially fatal hypersensitivity reaction. Anaphylaxis represent a clinical diagnosis based on history and physical examination and includes symptoms of airway obstruction, generalized skin reactions, particularly flushing, itching, urticaria, angioedema cardiovascular symptoms including hypotension and gastrointestinal symptoms. These symptoms result from the action of mast cell mediators, especially histamine and lipid mediators such as leukotrienes and platelet activating factor on shock tissue. The shock tissue includes blood vessels, mucous glands, smooth muscle, and nerve endings. Anaphylaxis follows the typical immediate hypersensitivity time course, with a reaction beginning within minutes of antigen exposure. A late-phase reaction hours after the initial reaction may occur. Mast cell mediator release can be triggered by both IgE and non--IgE-mediated factors. Therefore, anaphylaxis may be termed anaphylaxis (IgE mediated) or anaphylactoid (non--IgE mediated). The most common IgE-mediated triggers are drugs, typically penicillin or other beta-lactam antibiotics, foods, most commonly nuts, peanuts, fish and shellfish, or hymenoptera stings. Non-IgE-mediated causes include factors causing marked complement activation such as plasma proteins or compounds which act directly on the mast cell membrane, such as vancomycin, quinolone antibiotics, or radiographic contrast media. The pathophysiology of some trigger factors, such as aspirin, remains unclear. Therapy of anaphylaxis revolves around patient education, avoidance, desensitization or pharmacologic pretreatment when agents causing anaphylaxis need to be readministered, and early recognition and prompt therapy of reactions should they occur.