Which term describes a rare, unpredictable drug reaction that is not dose-dependent?

• A. Idiosyncratic action
• B. Iatrogenic
• C. Prophylaxis
• D. Receptor

Answer: (A)

Idiosyncratic reactions are rare, unpredictable drug responses that do not depend on the dose. They arise from individual factors such as genetic differences, metabolic quirks, or immune-mediated processes, so the reaction can occur at any dose and isn’t predictable from the drug’s normal pharmacology. This is why the pattern is described as idiosyncratic—the reaction is peculiar to the person rather than a direct, dose-related effect. For example, some patients may develop severe immune-mediated reactions to certain drugs regardless of how much is used. In contrast, iatrogenic describes harm caused by medical treatment itself, which is about the context of care rather than the nature of the reaction; prophylaxis means preventive therapy; and receptor refers to the drug’s molecular target, not a description of adverse reactions.