Anaphylactoidlike

Anaphylactoidlike is a term used to describe clinical reactions that resemble anaphylaxis but are not mediated by IgE antibodies. The phrase implies a phenotype of rapid, systemic mediator release that produces similar signs and symptoms to anaphylaxis, yet the underlying mechanism does not involve traditional IgE sensitization.

Pathophysiology commonly involves non–IgE-mediated mast cell and basophil activation. Triggers can include direct mast cell degranulation by certain drugs (for example, some opioids or vancomycin), complement activation by contrast media, or other mediators such as kallikrein-kinin system activation. The result is release of histamine and other inflammatory mediators, causing vasodilation, increased vascular permeability, bronchospasm, urticaria, angioedema, hypotension, and, in some cases, gastrointestinal symptoms.

Clinically, an anaphylactoidlike reaction presents with a rapid onset of skin, respiratory, and/or cardiovascular symptoms, often within minutes to an hour of exposure to the trigger. It can be difficult to distinguish from IgE-mediated anaphylaxis based on history alone; management is therefore guided by the presenting signs and severity rather than mechanism.

Management follows protocols for anaphylaxis and includes prompt assessment of airway, breathing, and circulation. Key steps are administration of intramuscular epinephrine, airway support, supplemental oxygen, and intravenous fluids for hypotension. Adjunctive therapies may include antihistamines, corticosteroids, and vasopressors if needed. Identifying and removing the trigger is important, and slow or cautious re-exposure may be considered with appropriate precautions in future procedures.

Terminology varies, and modern practice often emphasizes mechanism-based language (IgE-mediated versus non–IgE-mediated) rather than the older “anaphylactoid” label. Anaphylactoidlike reactions are generally managed the same as other acute anaphylaxis-like emergencies.