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anaphylactoid reactionAn anaphylaxis-like reaction that occurs without an allergen-IgE antibody event, caused by a nonimmune release (e.g., reaction to radiocontrast, opiates, vancomycin, chymopapain, aspirin) of vasoactive and inflammatory mediators, including histamine.
anaphylactoid reaction(an″ă-fĭ-lak′′toyd″) [ anaphylact(ic) + -oid]
This relatively uncommon type of reaction can be caused by exercise; as the result of the release of histamine when body temperature rises; by elevated endorphin levels; by ionic compounds such as contrast media that contain radiographic iodine or polymyxin B antibiotic; by solutions containing polysaccharides such as dextran; by morphine, codeine, or meperidine; and by NSAIDs. The term should not be used as a synonym for mild anaphylaxis produced by IgE-allergen reactions.
Anaphylactoid reactions produce hives and itching identical to those of anaphylaxis. Very rarely, severe anaphylaxis or anaphylactic shock occurs. Anaphylactoid reactions are treated with the same drugs used to treat anaphylaxis.