Drug allergies

Drug allergies and adverse drug reactions (ADRs) are often discussed together in clinical practice, but they represent distinct entities in pharmacology. Drug allergies are a subset of ADRs that involve an immune-mediated response to a medication. These reactions occur when the immune system identifies a drug as a harmful substance, leading to allergic responses such as hives, itching, swelling, or in severe cases, anaphylaxis. Drug allergies are typically unpredictable and can manifest even after exposure to very small doses of a drug, particularly if the patient has been previously sensitized.

In contrast, ADRs encompass all unintended and harmful effects of a drug, regardless of whether they involve the immune system. ADRs can be dose-dependent (e.g., excessive sedation from benzodiazepines) or dose-independent (e.g., drug-induced liver injury), and they can be predictable or unpredictable based on the drug’s pharmacological properties.

While both drug allergies and ADRs result in undesirable effects, the key difference is that drug allergies specifically involve an immune response, whereas ADRs are a broader category that includes any adverse effect of a drug, immune-mediated or not. Understanding this distinction is essential for proper diagnosis, management, and prevention of both drug allergies and ADRs in clinical settings.

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