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Causes
By Mayo Clinic staffA drug allergy occurs when your immune system mistakenly identifies a drug as if it were a harmful substance instead of a helpful remedy. Your immune system then reacts to the medication. Chemicals released by this reaction cause the signs and symptoms associated with an allergic reaction.
It isn't clear why some people develop drug allergies or other adverse drug reactions while others don't. Inherited traits may play a role, along with environmental factors and taking a number of medications over time.
Antibiotic allergy
Drug allergies are often caused by penicillin, antibiotics closely related to penicillin and antibiotics that contain sulfonamides. Antibiotics can also cause nonallergic reactions such as nausea or diarrhea.
Vaccine allergy
Rarely, allergic reactions occur after vaccination. In certain cases, allergic reactions may be caused by the vaccine itself, but more often an allergic reaction is triggered by other ingredients in the vaccine such as egg or neomycin. Nonallergic reactions to vaccines, such as redness and itching, are common, but in most cases they aren't severe and symptoms improve quickly.
Nonallergic adverse reactions
In many cases, what appears to be a drug allergy is actually a reaction that doesn't involve the immune system. Although they may seem like an allergy, drug reactions may be a drug side effect or signs of a drug sensitivity — not an allergic reaction.
Some examples of drugs that commonly cause nonallergic reactions include:
- X-ray contrast. Some people are sensitive to intravenous (IV) contrast used in some X-ray tests. This reaction can cause itching, flushing and a drop in blood pressure.
- Aspirin and other pain relivers. In some people, aspirin, ibuprofen (Advil, Motrin, others), naproxen (Aleve, Naprosyn, others) and others, can cause breathing trouble, wheezing and hives.
- Antibiotics. Some antibiotics often cause reactions such as stomachache or diarrhea.
- High blood pressure medication. Angiotensin-converting enzyme (ACE) inhibitors sometimes cause coughing and swelling of the lips, tongue and face.
- Celik J. Drug allergy. In: Adkinson NF. Middleton's Allergy: Principles and Practice. 7th ed. Philadelphia, Pa.: Mosby Elsevier; 2008. http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-0-323-05659-5..00068-1&isbn=978-0-323-05659-5&uniqId=281389325-3#4-u1.0-B978-0-323-05659-5..00068-1. Accessed Sept. 12, 2011.
- Medications and drug allergic reactions: Tips to remember. American Academy of Allergy, Asthma & Immunology. http://www.aaaai.org/conditions-and-treatments/library/at-a-glance/medications-and-drug-allergic-reactions.aspx. Accessed Sept. 12, 2011.
- Drug hypersensitivity. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/immunology_allergic_disorders/allergic_and_other_hypersensitivity_disorders/drug_hypersensitivity.html#v996144. Accessed Sept. 12, 2011.
- Pichler WJ, et al. Drug hypersensitivity reactions: Pathomechanism and clinical symptoms. Medical Clinics of North America. 2010;94:645.
- Granowitz EV, et al. Antibiotic adverse reactions and drug interactions. Critical Care Clinics. 2008;24:421.
- Possible side-effects from vaccines. Centers for Disease Control and Prevention. http://www.cdc.gov/VACCINES/vac-gen/side-effects.htm. Accessed Sept. 12, 2011.
- Scherer K, et al. Danger signs in drug hypersensitivity. Medical Clinics of North America. 2010;94:681.
- Romano A, et al. Recent advances in the diagnosis of drug allergy. Current Opinion in Allergy and Clinical Immunolgy. 2007;7:299.
- Aberer W, et al. Provocation tests in drug hypersensitivity. Immunology and Allergy Clinics of North America. 2009;29:567.
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