Allergies to Drugs

People sometimes mistake many adverse drug reactionsOverview of Allergic Reactions

Allergic (usually hypersensitivity) reactions to drugs (including medications) 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 (see Allergic Reactions: Introduction). These reactions range from minor and simply annoying to severe and life threatening. Examples are

• Rashes and itching

• Fever

• Constriction of the airways and wheezing

• Swelling of tissues (such as the voice box [larynx] and the opening between the vocal cords that closes to stop the flow of air to the lungs [glottis]), which impairs breathing

• Fall in blood pressure, sometimes to dangerously low levels

Other types of allergic reactions to drugs are even less common than hypersensitivity reactions. They usually take days or weeks to develop and tend to last longer. These reactions involve different types of antibodies that react with a drug and attack different parts of the body. For example, they can affect red blood cells and lead to anemia or cause inflammation that can affect the skin, joints, or kidneys.

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 anaphylactic reaction

Before prescribing a new medication, doctors usually ask whether a person has any known drug allergies. People who have had severe allergic reactions should wear a medical 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.