Drug allergies

Definition

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

Alternative Names

Causes

In general, adverse reactions to drugs are not uncommon, 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.

True drug allergies occur when there is an allergic reaction to a medication. The first time you take the drug, your immune system launches an incorrect response against a substance that is harmless in most people. The second or next time you take the drug, an immune response occurs, and your body produces antibodies and histamine.

Most drug allergies cause minor skin rashes and hives. However, other symptoms occasionally develop and life-threatening acute allergic reaction involving the whole body 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
• Anticonvulsants
• Insulin preparations (particularly animal sources of insulin)
• Local anesthetics such as Novocain
• Iodine (found in many x-ray contrast dyes)

Some drug reactions are considered idiosyncratic. This means the reaction is an unusual effect of the medication. For example, aspirin can cause nonallergic hives or trigger asthma. Only a small number of these reactions are allergic in nature. Many individuals may confuse an uncomfortable but not serious side effect of a medicine, such as nausea, with a true drug allergy, which can be life threatening.

References

Adkinson NF Jr. Middleton’s Allergy: Principles and Practice. 6th ed. Chapter 92. Philadelphia, Pa: Mosby; 2003.