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Penicillin Allergy

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View a list of insurance plans accepted at the University of Miami Health System.

You have a penicillin allergy if your immune system reacts abnormally when you take penicillin or any medicine containing penicillin. Signs and symptoms of penicillin allergy usually occur within an hour of taking a medication containing the substance. In some cases, you may experience symptoms hours, days, or even weeks later.

Signs and symptoms of penicillin allergy include:

  • Skin rash
  • Hives
  • Itching
  • Fever
  • Swelling
  • Shortness of breath
  • Wheezing
  • Runny nose
  • Itchy, watery eyes
  • Anaphylaxis*

*You should call 911 immediately or go to the nearest hospital emergency room if you experience this serious symptom.


If your body is currently reacting to penicillin but your reaction is not life-threatening, your doctor may prescribe an antihistamine or recommend an over-the-counter antihistamine (Benadryl) that can block immune system chemicals that are activated during an allergic reaction.

In the case of more serious reactions, your doctor may recommend oral (by mouth) or injected corticosteroids to treat inflammation associated with penicillin allergy.

Drug Desensitization
If you need to take penicillin or a penicillin-containing medication and no alternatives are available, your doctor may recommend you undergo drug desensitization under their close supervision. This involves taking a very small dose of penicillin, and then progressively larger doses every 15 to 30 minutes over the course of several hours or a few days. If you reach the desired dose with no reaction, you can continue the treatment with penicillin.


Comprehensive Exam
Your doctor will perform a comprehensive physical exam – including a health history – to help diagnose your penicillin allergy.

Skin Test
Your allergist will inject a tiny amount of penicillin into your skin in a controlled environment and then watch for an allergic reaction. If you are allergic to penicillin, a red, itchy, raised bump will appear.

Why Choose UHealth?

Expert care with a personal touch. Our doctors are dedicated to spending as much time with you as you need and not rushing you through your visit. We answer all the questions you may have and provide you with the techniques and knowledge to help you get the most out of your medications. We’ll explain your laboratory results and how the medicine will impact the causes and symptoms of your condition and improve your quality of life.