A drug allergy is the abnormal reaction of your immune system to a medication. Reactions range from irritating or mild side effects such as nausea and vomiting to life-threatening anaphylaxis. A true drug allergy is caused by a series of chemical steps in the body that produce the allergic reaction to a medication.
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 you are exposed to a medication or vaccine. Allergy-causing drugs include anticonvulsants, insulin, iodinated x-ray contrast dyes, Penicillin and related antibiotics, sulfa drugs. Penicillin causes most allergic drug symptoms. Common symptoms of a drug allergy include hives, itching of the skin or eyes, skin rash, swelling of the lips, tongue, or face, wheezing. Anaphylaxis, a potentially life-threatening reaction that can impair breathing and send the body into shock; reactions may simultaneously affect two or more organ systems. Signs and symptoms of anaphylaxis include tightening of the airways and throat, causing trouble breathing, nausea or abdominal cramps, vomiting or diarrhea, dizziness or lightheadedness, rapid pulse, drop in blood pressure.
The various interventions used to treat an allergic reaction to a drug include withdrawal of the drug, discontinuing the drug is the first step in treatment. Antihistamines, over-the-counter antihistamine such as diphenhydramine (Benadryl) that can block immune system chemicals activated during an allergic reaction. Corticosteroids, either oral or injected corticosteroids may be used to treat inflammation associated with more-serious reactions. Anaphylaxis requires an immediate epinephrine injection as well as hospital care to maintain blood pressure and support breathing.