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Drug Allergy (cont.)

Drug Allergy Causes

An allergic reaction is caused by the body's immune system overreacting to the drug, which is viewed as a chemical "invader," or antigen. This overreaction is often called a hypersensitivity reaction.

  • The body produces antibodies to the antigen and stores the antibodies on special cells.
  • The antibody in an allergic reaction is called immunoglobulin E, or IgE.
  • When the body is exposed to the drug again, the antibodies signal the cells to release chemicals called "mediators." Histamine is an example of a mediator.
  • The effects of these mediators on organs and other cells cause the symptoms of the reaction.

The most common medication allergies are:

Risk factors for drug allergies include:

  • Frequent exposure to the drug
  • Large doses of the drug
  • Drug given by injection rather than pill
  • Family tendency to develop allergies and asthma
  • Certain food allergies such as to eggs, soybeans, or shellfish
Medically Reviewed by a Doctor on 7/30/2014

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Drug eruptions can mimic a wide range of dermatoses. The morphologies are myriad and include morbilliform (most common, see Media file 1), urticarial, papulosquamous, pustular, and bullous. Medications can also cause pruritus and dysesthesia without an obvious eruption.

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