Drug allergies

Alternative names:

allergic reaction to a drug (medication)

Definition:

A group of symptoms caused by allergic reaction to a drug (medication).

Causes, incidence, and risk factors:

Drug allergies occur when there is an allergic reaction to a medication. This is caused by hypersensitivity of the immune system, leading to a misdirected response against a substance that does not cause a response in most people. The body becomes sensitized (the immune system is triggered) by the first exposure to the medication. The second or subsequent exposure causes an immune response.

Reactions to drugs are uncommon, but almost any drug can cause an adverse reaction. Reactions range from irritating or mild side effects (such as nausea and vomiting), to allergic response including life-threatening anaphylaxis. Some drug reactions are idiosyncratic (unusual effects of the medication). For example, aspirin can cause nonallergic hives (no antibodies formed), or it may trigger asthma.

"True" drug allergies involve the production of antibodies and the release of histamine and other chemicals. Most drug allergies cause minor skin rashes and hives. However, other symptoms occasionally develop and life-threatening acute allergic reaction involving the whole body (anaphylaxis) can occur. Serum sickness is a delayed type of drug allergy that occurs a week or more after exposure to a medication or vaccine.

Penicillin and related antibiotics are the most common cause of drug allergies. Other common allergy-causing drugs include sulfa drugs, barbiturates, anticonvulsants, insulin preparations (particularly animal sources of insulin), local anesthetics such as Novocain, and iodine (found in many X-ray contrast dyes).