anaphylactoid reaction

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Related to anaphylactoid reaction: anaphylaxis, Anaphylactic reaction


resembling anaphylaxis.
anaphylactoid reaction a reaction resembling generalized anaphylaxis but not caused by IgE-mediated allergic reaction but rather by a nonimmunologic mechanism.

anaphylactoid reaction

An 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]
A reaction that resembles anaphylaxis, e.g., by hives, laryngeal edema, or shock, but does not involve IgE antibodies or allergens and therefore is has no allergic basis.


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.

References in periodicals archive ?
It was concluded that many heroin fatalities might be due to anaphylactoid reactions mediated by the direct action of heroin, liberating mediators such as histamine and tryptase from mast cells.
We wish to thank Dr Russell for his interest in our recent case report addressing unrecognised mastocytosis in a patient manifesting as an anaphylactoid reaction to the administration of iodinated radiocontrast material (1).
Similar profiles of adverse events and anaphylactoid reactions have been reported in each of the European clinical trials of sodium ferric gluconate complex (Faich & Strobos, 1999).
Tryptase levels peak approximately one hour after an anaphylactic or anaphylactoid reaction has begun and slowly return to normal baseline levels after 8 to 12 hours.
The Danish Anaesthesia Allergy Centre established in 1998 investigated 36 subjects who suffered anaphylactoid reactions referred to it up to July 2001 (67).
One of the 16 had an anaphylactoid reaction to morphine infusion, while the other 15 were determined to have had anaphylaxis secondary to operative exposures.
Anaphylactic reactions may not be clinically distinguished from anaphylactoid reactions.
EPP is a poorly characterised and an ultra-rare metabolic disorder which causes severe phototoxic and anaphylactoid reactions in patients.
Although the hemodynamic changes occurring during anaphylaxis and anaphylactoid reactions may vary, the major factors causing cardiovascular abnormalities are universal and result from an initial loss of intravascular fluid and vasodilation, which may be followed shortly by vasoconstriction and then myocardial depression.
Anaphylactic or anaphylactoid reactions may also be secondary to complement activation with liberation of anaphylatoxins.