Common Drug Allergies: Mild to Fatal

Tell your doctor about allergic reactions to medications

doctor and patient discussing medication in office
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Reactions to medication are extremely common and 15-30 percent of all hospitalized patients will experience an unintended reaction as a result of medications. However, true allergic reactions to medications only occur in about 1 in 10 of all adverse drug reactions.

People can experience allergic reactions to just about any medication.

Classification of Reactions to Medications

Before we can discuss the huge topic of medication allergy, we need to group reactions to drugs into one of 2 categories:

  • Reactions which are common and predictable in any person represent the majority of all reactions to medications.
  • Reactions which are unpredictable, and only occur in certain people. 

Allergic Reactions to Medications

True allergic reactions to medications typically follow certain features:

  • The first time you took it there was no reaction.
  • The reaction from the medication is different from expected side effects.
  • The reaction is suggestive of allergy or anaphylaxis.
  • The symptoms of the reaction disappear within a few days after you stop taking it. 

Symptoms of Allergic and Immunologic Reactions

Skin rashes are the most common symptoms of adverse drug reactions. Urticaria and angioedema suggest an allergic cause, while blistering, peeling and sunburn-like reactions suggest non-allergic immunologic causes. 

Other non-allergic immunologic symptoms can include:

  • fever
  • kidney failure
  • hepatitis
  • blood problems (such as anemia)

    Drug Allergy to Penicillin

    About 1 in every 10 people reports a history of an “allergic reaction” to penicillin, but much less than 10 percent of those who think they are allergic to penicillin actually are.

    A true allergy to penicillin could have life-threatening anaphylaxis as a result.

    Drug Allergy to Cephalosporins

    Severe reactions to cephalosporins, a class of antibiotic, are much less common than with penicillins.

    However, there is a small chance if you have a true penicillin allergy you could also react to cephalosporins.

    Drug Allergy to NSAIDs

    Non-steroidal anti-inflammatory drugs (NSAIDs) include pain relievers such as aspirin, ibuprofen, and naproxen. They can:

    • cause allergic and non-allergic flares of hives/swelling
    • worsen asthma
    • result in anaphylaxis

    A Reaction to IV Contrast Dye

    The reaction to IV contrast dye is non-allergic but can result in anaphylaxis because the high concentration of the dye causes mast cells to release their contents, which mimics an allergic reaction. However, most patients can take the dye safely by using oral steroids and anti-histamines hours before the contrast is given. 

    Drug Allergy to Local Anesthetics

    True allergic reactions to local anesthetics (novocaine, lidocaine) are extremely rare, and usually due to other ingredients in the medication, such as preservatives or epinephrine.

    Non-Allergic Reactions to Anti-Seizure Medications

    Many anti-seizure medications used for epilepsy treatment cause non-allergic reactions as a result of certain enzyme deficiencies in the person taking the medication. Symptoms can include:

    • a rash
    • fever
    • body aches
    • hepatitis

    Learn about the treatment for allergic drug reactions.

    DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.


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