Table 2

Classification of allergic drug reactions: mechanisms, clinical manifestations, and timing of reactions. [7-9]

Immune reaction


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


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

IgE: immunoglobulin E; IgG: immunoglobulin G; IgM: immunoglobulin G; MHC: major histocompatibility complex

*These reactions may also be non-immunologically mediated.

Adapted from Riedl et al., 2003.6

Warrington and Silviu-Dan Allergy, Asthma & Clinical Immunology 2011 7(Suppl 1):S10   doi:10.1186/1710-1492-7-S1-S10

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