Drug allergy differential diagnosis
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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Overview
Differentiating Drug Allergy from Other Drug Reactions
Pseudoallergic Reactions
There are reactions called pseudoallergic reactions which, are in the category of adverse drug reactions. Although they mimic drug allergies, immunologic mechanisms have not been demonstrated as an underlying cause. There are also reactions called non-immunologic hypersensitivity reactions for which immunologic mechanisms of reactions have also not been demonstrated.
Some pseudoallergic reactions occur as a result of direct activation of immune cells and inflammatory cells, so the final steps of pathogenesis are the same and the clinical features are similar. Despite the similarities, the diagnosis, prognosis and future prevention are different.
Non-immunologic anaphylaxis can also occur. All types of anaphylaxis are life-threatening. The term “anaphylactoid reaction” often used for non-immunologic anaphylaxis can sometimes be interpreted as less severe, although this is not true. Some patients who show marked dermographism, have profound mast cell instability, which is thought associated with pseudoallergic reactions.
Some agents commonly implicated in pseudoallergic reactions are;
- NSAIDS
- vancomycin
- local anesthetics
- radiocontrast agents
- opiates
- chemotherapeutics
- monoclonal antibodies and other biologic therapies used in cancer treatment
Auto-immune Like Syndromes Caused by Drugs
Lupus like syndromes can be caused by the following medications;
A pemphigus like syndrome can be caused by penicillamine
IgA bullous dermatitis can be caused by:
Differentiating Drug Allergy from Other Conditions
IgE Mediated Drug Allergies
Certain IgE mediated conditions need to be differentiated from IgE mediated drug allergies (angioedema, urticaria, anaphylaxis, bronschospasm);
- Insect bites and stings
- Carcinoid syndrome
- Asthma
- Food allergy
- Latex allergy
- Scombroid fish poisoning
- Mastocytosis
- Infection (EBV, gastrointestinal parasites, hepatitis A, hepatitis B, and hepatitis C