Drug Allergies - Managing Your Allergies: Allergies
Content provided by the Faculty of the Harvard Medical School
Drug allergies
Every FDA-approved drug carries a warning of possible side effects. Allergic reaction is one such side effect. While many drug side effects are predictable to some degree, an allergic reaction is unpredictable. Although it can happen out of the blue, an allergic reaction to a drug is rarely fatal. However, it can cause considerable discomfort and distress in the form of hives, difficulty breathing, fever, swelling, tender glands, itchy rash, and anaphylaxis.
Although any drug can potentially trigger an allergic response, some drugs have been recognized as more allergenic. Of these, the “big three” are penicillin, certain other antibiotics, and aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs). Aspirin and NSAIDs are responsible for allergy-type reactions, but they do it “their way” by engaging mast cells and triggering the response without involving IgE. In fact, several drugs cause reactions that are identical to allergic reactions but without IgE. Examples include intravenous x-ray dyes, paclitaxel, vancomycin, opiates such as morphine, and ACE inhibitors. However, the symptoms look similar in both types of reactions.
Allergenic drugsAny drug can cause an allergic reaction, but the drugs listed below have been recognized as more likely to do so. | |||
| Antibiotics
Aspirin and NSAIDs
| Monoclonal antibodies
| Insulin
Anticonvulsants
| ACE inhibitors Anesthetic agents Blood products Opiates X-ray dyes |
Diagnosing drug allergies
If you’ve reacted in the past to a drug, it’s highly likely that the same thing will happen on a subsequent exposure. You’re also more likely to have a reaction to a drug if you’ve previously reacted to another drug that has what’s called “cross-reactivity” with it. For example, allergy to penicillin carries a 15% risk for allergy to first-generation cephalosporins.
For drug allergy, a detailed history is crucial. When did the reaction occur? What drugs were you taking? How soon after taking the drugs did you have the reaction? What kind of reaction did you have? How severe was the reaction, and how long did it last? If you had a rash, did it blister, peel, or cause ulcers in the mouth, vagina, or rectum? Have you since taken that drug or one like it without a reaction? If you’re not sure what drugs you’re allergic to, there are skin tests for some but not all of the likely suspects.
Treating drug allergies
If you’ve had a reaction to a drug, make sure to tell your doctor. The best approach is not to take the drug. In almost all instances, an alternative can be prescribed. When this isn’t possible, a lowered dose or gradual introduction of the drug — that is, desensitization to the drug — may circumvent the problem. But never attempt this on your own! Desensitization might be used, for example, in the case of an antibiotic for a life-threatening infection, chemotherapeutic agents such as paclitaxel or carboplatin, or aspirin in aspirin-sensitive asthma. However, there are some reactions for which desensitization must never be attempted. These include serum sickness and some rashes such as erythema multiforme or Stevens-Johnson syndrome.
| Last updated: | August 21, 2006 |
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| Reviewed By: | Faculty of Harvard Medical School |
Medical content reviewed by the Faculty of the Harvard Medical School. Harvard Health Publications, Copyright © 2007 by President and Fellows of Harvard College. All rights reserved. Used with permission of StayWell.
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