Drug allergies and mechanisms

Framing

Drug allergy encompasses true immune-mediated reactions (IgE-mediated immediate hypersensitivity, delayed T-cell-mediated reactions) and non-immune pseudo-allergic reactions (e.g. direct mast cell activation) - accurate mechanistic classification determines both acute management and whether future re-exposure/cross-reactivity risk applies
Distinguishing a genuine drug allergy from a predictable adverse drug effect (dose-dependent toxicity, intolerance) matters clinically, since mislabelled "allergy" (particularly penicillin allergy labels) leads to unnecessary avoidance of first-line, more effective antimicrobial therapy

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