Definition of Drug allergies:

Drug allergies are a group of symptoms caused by an allergic reaction to a drug (medication).

Causes, incidence, and risk factors:

Adverse reactions to drugs are common, and almost any drug can cause an adverse reaction. Reactions range from irritating or mild side effects such as nausea and vomiting to life-threatening anaphylaxis.

A true drug allergy results from a series of chemical steps within the body that produce the allergic reaction to a medication.

It can develop two different ways:

1. The first time you take the medicine, you have no problems, but your body's immune system produces a substance (antibody) called IgE against that drug. The next time you take the drug, the IgE tells your white blood cells to make a chemical called histamine, which causes your allergy symptoms.
2. A drug allergy may also occur without your body producing IgE, but this is not well understood.

Most drug allergies cause minor skin rashes and hives. 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
• Anticonvulsants
• Insulin preparations (particularly animal sources of insulin)
• Iodinated (containing iodine) x-ray contrast dyes (these can cause allergy-like anaphylactoid reactions)

Most side effects of drugs are not due to an allergic reaction. For example, aspirin can cause nonallergic hives or trigger asthma. Some drug reactions are considered "idiosyncratic." This means the reaction is an unusual effect of the medication, not due to a predictable chemical effect of the drug. Many people confuse an uncomfortable, but not serious, side effect of a medicine (such as nausea) with a true drug allergy, which can be life threatening.