Following ingestion of a particular medication, the body sometimes responds by signaling the immune system to produce an allergic reaction, which can be mild, or life threatening.
Occasionally, when a drug enters the body (by swallowing, contact with the skin, inhaled or injected) the immune system recognizes that substance as foreign and triggers a heightened response causing a multitude of allergic symptoms. The immune system uses protective antibodies that are already present to fight the offending agent. Someone who is allergic to a drug has an overabundance of these antibodies against a particular drug. This is why it is possible to have an allergic reaction even after already taking the drug before without a noticeable reaction; the body can build up these antibodies over time. The antibody immunoglobulin E, or IgE, begins the process of an allergic reaction and then triggers cells to release chemicals such as histamine. Histamine is actually the chemical response for the side effects that take place during an allergic reaction.
Symptoms of an allergic reaction include rashes, hives, swelling of the face, eyes or tongue, difficulty swallowing or breathing, and dizziness or fainting. It is important not to panic if you are experiencing an allergic reaction as anxiety can worsen the symptoms. For a mild reaction such as rash or hives, your doctor or pharmacist might recommend an anti-histamine like Benadryl® (diphenhydramine) to lessen the effects of circulating histamine. For more serious reactions, swelling of the throat or tongue with difficulty breathing, immediate medical help should be first priority. If you are unsure if symptoms are an allergic reaction versus normal side effects, please call your local pharmacist.
Whenever you have a prescription filled, always present a list of known drug allergies.
Dr. Melissa Vice, PharmD.