Classification of unpredictable adverse drug reactions1,8
| Classification | Description | Example |
|---|---|---|
| Intolerance | Occurs at very low doses and is not due to underlying abnormalities of metabolism, bioavailability or excretion | ASA-induced tinnitus |
| Idiosyncracy | Unrelated to intended pharmacologic action of the drug, is reproducible, and is usually due to abnormalities of metabolism, excretion or bioavailability | Primaquine-induced hemolytic anemia in glucose-6-phosphate dehydrogenase deficiency |
| Allergy | Immune mediated: Type 1 (IgE-mediated) Type 2 (cytotoxic) Type 3 (immune complex) Type 4 (delayed hypersensitivity; subclassified into monocytes (IVa), eosinophils (IVb), CD8+ T lymphocytes (IVc), neutrophils (IVd) | Type 1: anaphylaxis Type 2: thrombocytopenia, anemia Type 3: serum sickness, vasculitis Type 4: benign drug exanthems, DRESS, AGEP, contact dermatitis |
| “Pseudoallergy” | Similar to type I allergic reactions with different pathophysiology (direct mediator release, often histamine, from mast cells and basophils) | Opiate-induced urticaria |
Note: AGEP = acute generalized exanthematous pustulosis, ASA = acetylsalicylic acid, DRESS = drug reaction with eosinophilia and systemic symptoms, IgE = immunoglobulin E.