Drug Allergies
Allergic (hypersensitivity) reactions to a drug are relatively uncommon. In contrast to other types of adverse drug reactions, the number and severity of allergic reactions do not usually correlate with the amount of drug taken. For people who are allergic to a drug, even a small amount of the drug can trigger an allergic reaction. These reactions range from minor and simply annoying to severe and life threatening (see Section 16, Chapter 185). Examples are skin rashes and itching; fever; constriction of the airways and wheezing; swelling of tissues (such as the larynx and glottis), which impairs breathing; and a fall in blood pressure, sometimes to dangerously low levels.
Drug allergies cannot be anticipated, because reactions occur after a person has been previously exposed to the drug (whether it was applied to the skin, taken by mouth, or injected) one or more times without any allergic reaction. A mild reaction may be treated with an antihistamine; a severe or life-threatening reaction may require an injection of epinephrine (also called adrenaline) or a corticosteroid, such as hydrocortisone.
Before prescribing a new drug, doctors usually ask if a person has any known drug allergies. People who have had severe allergic reactions should wear a Medic Alert necklace or bracelet inscribed with their drug allergies. This information (for example, penicillin allergy) can alert medical and paramedical personnel in case of an emergency.
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