Penicillin Allergy

Nearly everyone knows someone who says they are allergic to penicillin. Up to 10 percent of people report being allergic to this widely used class of antibiotic, making it the most commonly reported drug allergy. Over time, however, the vast majority of people who once had a allergic reaction to penicillin lose sensitivity and can be treated safely with the drug.

Understanding penicillin allergies is important for a variety of reasons. For certain conditions, penicillin is the best (or only proven) therapy. Some patients need penicillin because they are allergic to other types of antibiotics. Allergists may want to know if childhood allergic reactions persist in their adult patients, to establish more complete medical histories and treatment options.

Penicillin Allergy Symptoms

Allergic reactions to penicillin are common, and symptoms may include:

  • Hives (raised, extremely itchy spots that come and go over a period of hours)
  • Tissue swelling under the skin, typically around the face (also known as angioedema)
  • Throat tightness
  • Wheezing
  • Coughing

A less common but more serious allergic reaction is anaphylaxis which occurs in highly sensitive patients. Anaphylaxis occurs suddenly, can worsen quickly and can be deadly. Symptoms might include hives, swelling and throat tightness listed above, but also any of the following: 

  • Tightness in the chest and difficulty breathing
  • Swelling of the tongue, throat, nose and lips
  • Dizziness and fainting or loss of consciousness, which can lead to shock and heart failure

These symptoms require immediate attention at the nearest Emergency Room. The first line of treatment for anaphylaxis is epinephrine. If you have been prescribed an epinephrine auto-injector, use it right away, then seek follow-up medical care. If you do not have an auto-injector available, call 911 or go to the emergency room immediately.


Penicillin Allergy Testing and Diagnosis

 Read more: Penicillin Testing: A Patient’s Story

An allergist can help you evaluate the safety of taking penicillin.

In addition to assessing your detailed history about a prior allergic reaction to penicillin, allergists administer skin tests to make an accurate diagnosis. These tests, which are conducted in an office or a hospital setting, typically take about two to three hours.

When safely and correctly administered, skin tests involve pricking the skin, injecting a weakened form of the drug, and observing the patient’s reaction. Those with positive allergy skin tests should avoid penicillin and be treated with a different antibiotic in the future.

People who react negatively to the injection are considered to be at low risk for an immediate acute reaction to the medication. The allergist might then give these individuals a single, full-strength oral dose to confirm the absence of a penicillin allergy.

If penicillin is essential treatment for an illness, people in some cases can undergo penicillin desensitization to enable them to receive the medication in a controlled manner under the care of an allergist.

Reprinted and revised with permission from the American College of Allergy, Asthma & Immunology; www.acaai.org