Which of the following adverse drug reactions occurs most rapidly?
Type I - IgE mediated reactions occur within minutes to hours after exposure.
Immunologic adverse drug reactions
Immune-mediated reactions account for 5 - 10% of all adverse drug reactions. The Gell and Coombs system is used to classify these types of reactions. This system classifies reactions into the following groups:-
1) Type I (IgE-mediated) reactions
2) Type II (cytotoxic) reactions
3) Type III (immune complex) reactions
4) Type IV (cell mediated) reactions
Type I reactions
These arise when a drug-IgE complex binds to mast cells with a release of histamine and other inflammatory mediators. They characteristically cause anaphylaxis, urticaria, and bronchospasm. They generally occurs minutes to hours after exposure.
Type II reactions
These occur when a IgG or IgM antibody binds to a cell which has been altered by a drug-hapten. They often manifest as blood abnormalities such as thromboctopenia and neutropenia. The timing of these reactions is variable.
Type III reactions
These occur when drug-antibody complexes activate the complement system. They present with fever, rash, urticaria and vasculitis. These occur 1 to 3 weeks after exposure.
Type IV reactions
These arise when the MHC system presents drug molecules to T cells. They result in allergic contact dermatitis and rashes. They occur 2 to 7 days after cutaneous exposure
