• Description: an IgE-independent reaction that is clinically indistinguishable from type I hypersensitivity reaction
• Etiology
  • Radiocontrast media
  • Narcotics
  • Opioids
  • Vancomycin, NSAIDs
    • Red man syndrome (Vancomycin flushing reaction)
• Pathophysiology
  • Substances cause direct (or complement-mediated in case of anaphylactoid reaction) mast cell activation and subsequent release of histamine not mediated by immunoglobulin.
  • In contrast to true anaphylactic reactions, no sensitization to allergens is required (i.e., first contact can already lead to anaphylactic shock)
• Clinical features: urticaria, pruritus, edema, hypotension, or even symptoms of anaphylactic shock