Drug allergy overview
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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Drug Allergy |
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Diagnosis |
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Treatment |
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Overview
A drug allergy, or immunologic drug reaction is a reaction to a drug that specifically occurs through immunologic activation in response to a drug. Drug allergy is a sub-classification of adverse drug reactions. Adverse drug reactions are classified into two categories; Type A (predictable), and Type B (unpredictable). Drug allergy falls under Type B adverse drug reactions, along with pseodoallergic drug reactions.
Classification
Drug allergies are classified using two main sets of criteria. One is set forth by the World Allergy Association, and classifies the reaction as to whether it occurs within one hour of treatment, or after one hour. The other set of criteria are based on the type of immunologic reaction that occurred and the mediators involved.
Pathophysiology
An allergic reaction will not occur on the first exposure to a substance. The first exposure allows the body to create antibodies and memory lymphocyte cells for the antigen. However, drugs often contain many different substances, including dyes, which could cause allergic reactions. This can cause an allergic reaction on the first administration of a drug. For example, a person who developed an allergy to a red dye will be allergic to any new drug which contains that red dye. Medications can cause allergic reactions through various mechanisms. The drug can either act as a direct antigenic particle, or it can cause activation of immune cells by the direct interaction with immune cell receptors.
Causes
The types of drugs that can cause drug allergies vary. Drugs containing sulfa are common in causing drug allergy reactions. Other common drugs implicated in leading to an allergic reaction are antibiotics, insulin, and iodinated drugs.
Differentiating Drug Allergy from other Diseases
A drug allergy is different from an intolerance. A drug intolerance, which is often a milder, non-immune-mediated reaction, does not depend on prior exposure. Most people who believe they are allergic to aspirin are actually suffering from a drug intolerance.
Epidemiology and Demographics
Adverse drug reactions may occur in up to 10% of the worldwide population, and also affect up to 20% of patients who are hospitalized. Of all the cases of fatalities caused by anaphylaxis, drugs may be responsible for 20% of the deaths.
Risk Factors
There are known risk factors for the development of drug allergies. Some are based on the patient and include; female gender, being young or middle aged, genetics, presence of certain viral infections (HIV and EBV), and history of atopy or prior drug allergies. Other factors are based on the quality of the drug, and include; high molecular weight compounds, intravenous and intramuscular routes of administration, and frequent, prolonged, high doses of medication.