Drug allergy classification
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Charmaine Patel, M.D. [2]
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Classification Based on Timing of Symptoms
There are recommendations on the classification of drug allergy reactions based on the World Allergy Association (WAO) guidelines. The two categories of classification are based on whether the reaction occurs less than one hour of medication administration, or more than one hour afterwards.
- Immediate- these reactions occur within one hour, and are most likely due to IgE mediated type I reactions. At times, type I reactions can occur after one hour if the absorption of the drug is delayed, for example due to an oral medication or ingesting a medication with food. These types of reactions have the risk of anaphylaxis if the patient is re-exposed.
- Delayed-
Classification Based on Reaction Type
One type of classification of drug allergies, is based on the type of autoimmune process. This is the same type of classification that is used for other types of immunological reactions, and is based on the Gell and Coombs system. Drugs usually cause type III and type IV reactions, however certain medications such as penecillin, can cause all four.
- Type I hypersensitivity reaction: Immediate onset and primarily caused by the IgE, basophils, and degranulation of mast cells.
- Type II hypersensitivity reaction: Delayed onset reaction caused by antibodies, mediated by IgG mediated destruction of cells.
- Type III hypersensitivity reaction: Delayed in onset and caused by IgG immune complex formation and deposition, and complement activation.
- Type IV hypersensitivity reaction: T-cell mediated delayed onset reaction.