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Penicillin Allergy

What Is Penicillin?

Penicillin is a prescription antibiotic used to treat some infections, like strep throat. Penicillin (peh-neh-SIL-in) is part of a group of antibiotics that includes amoxicillin, ampicillin, and others. Because these antibiotics are alike, they’re called the penicillin family.

What Is a Penicillin Allergy?

Some people have allergic reactions to penicillin or other antibiotics in the penicillin family. Someone who is allergic to penicillin must avoid all antibiotics in the penicillin family.

Many people with a penicillin allergy outgrow it over time.

What Happens With a Penicillin Allergy?

When someone has a penicillin allergy, their immune system overreacts to the medicine. If they get penicillin or another antibiotic in the penicillin family, the body thinks these are harmful invaders and works hard to fight them. This causes an allergic reaction.

What Are the Signs & Symptoms of a Penicillin Allergy?

In an allergic reaction to a medicine in the penicillin family, the body releases chemicals like histamine, causing an allergic reaction. Reactions can be mild or severe. Even someone who has had mild reactions in the past can have a more serious one.

Signs of an allergic reaction can include:

  • hoarseness or throat tightness
  • belly pain, vomiting, or diarrhea
  • itching
  • hives or red spots
  • swelling of the face, hands, feet, throat, or tongue
  • coughing, wheezing, or trouble breathing
  • a drop in blood pressure, causing dizziness or loss of consciousness (passing out)

A penicillin allergy sometimes can cause a severe reaction called anaphylaxis. Anaphylaxis (an-eh-fih-LAK-siss) might start with some of the same symptoms as a less severe reaction, but quickly can get worse.

Someone with anaphylaxis needs to be treated with an epinephrine auto-injector right away. If you or your child have a penicillin allergy, ask your allergist if you should have epinephrine auto-injectors in case of emergency.

How Can Parents Help?

If allergy testing shows that your child has a penicillin allergy, an allergist will talk to you about how to keep your child safe.

The best way to prevent a reaction is to make sure your child avoids penicillin and other antibiotics in the penicillin family.

When Should I Call the Doctor?

If you think someone in your family has a penicillin allergy, see an allergist. Some people who think they have a penicillin allergy might not. An allergist can do testing to see who is truly allergic, or if someone outgrew an allergy.

You can learn more about penicillin allergies at:

    Reviewed by: Larissa Hirsch, MD
    Date Reviewed: Apr 1, 2023

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