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Table 2 Classification of allergic drug reactions: mechanisms, clinical manifestations, and timing of reactions. [79]

From: Drug allergy

Immune reaction Mechanism Clinical manifestations Timing of reaction
Type I (IgE-mediated) Drug-IgE complex binding to mast cells with release of histamine, inflammatory mediators Anaphylaxis*, urticaria*, angioedema*, bronchospasm* Minutes to hours after drug exposure
Type II (cytotoxic) Specific IgG or IgM antibodies directed at drug-hapten coated cells Anemia, cytopenia, thrombocytopenia Variable
Type III (immune complex) Tissue deposition of drug-antibody complexes with complement activation and inflammation Serum sickness, vasculitis, fever, rash, arthralgia 1 to 3 weeks after drug exposure
Type IV (delayed, cell mediated) MHC presentation of drug molecules to T cells with cytokine and inflammatory mediator release; may also be associated with activation and recruitment of eosinophils, monocytes, and neutrophils Contact sensitivity
Skin rashes, organ-tissue damage
2 to 7 days after drug exposure
  1. IgE: immunoglobulin E; IgG: immunoglobulin G; IgM: immunoglobulin G; MHC: major histocompatibility complex
  2. *These reactions may also be non-immunologically mediated.
  3. Adapted from Riedl et al., 2003.6