A _______ _______ is an immunologically mediated drug hypersensitivity reaction, which accounts for _____% of all adverse drug reactions.

• A. Idiosyncratic reaction; 1-2
• B. Hypersensitivity; 25-50
• C. Allergic reaction; 0.1-1
• D. Drug allergy; 5-10

Answer: (D)

Drug allergy is an immunologically mediated drug hypersensitivity reaction. It reflects an immune response to a medication that can range from mild rashes to severe anaphylaxis and usually requires prior sensitization. In the spectrum of adverse drug reactions, drug allergy accounts for about 5-10% of cases, making it a minority of ADRs. While hypersensitivity is the broad immunologic term, the specific immune-mediated form of this reaction due to a drug is most precisely called a drug allergy. Other ADRs are often non-immune, dose-related effects or idiosyncratic reactions that are not immune-mediated, which is why higher (25-50%) or much lower (0.1-1%, 1-2%) figures are not as accurate.