Drug Allergies

A drug allergy is a reaction that arises when the immune system develops an unexpected and excessive response to a medication being used. Not every rash or side effect that develops after taking a medication means a drug allergy. For this reason, making the correct diagnosis is very important — both to avoid unnecessary drug restrictions and to prevent serious reactions from recurring.

Drug allergies can present as itchy rashes, hives (urticaria), swelling of the lips and eyelids (angioedema), widespread redness, fluid-filled blisters, peeling of the skin and, more rarely, serious reactions that can be life-threatening. Findings may develop minutes after taking the medication, while some reactions may begin days or weeks later.

Drug allergies can occur with any medication; however, antibiotics, painkillers and antipyretics, and some medications used in the treatment of epilepsy are the most common causes. That said, not everyone who uses the same medication develops an allergy, and not every rash is caused by a drug.

In assessing a drug allergy, the appearance of the rash, when the medication was started, other medications being used, accompanying infections and the patient's history are all considered together. Where necessary, laboratory investigations, a skin biopsy or additional assessments in collaboration with the relevant specialties may be planned.

The first step in treatment is to stop the medication thought to be responsible and to start appropriate treatment according to the severity of the reaction. Because future re-exposure to the same or similar medications can lead to serious consequences, making the correct diagnosis and informing the patient appropriately is very important. Some skin conditions, viral infections and other allergic reactions can mimic drug allergy; for this reason a diagnosis should not be made on the presence of a rash alone, and the clinical findings should be assessed in detail.