News | Published April 1, 2019 | Written by Faoud Ishmael, MD, PhD, Mount Nittany Physician Group Allergy & Immunology

What you may not know about penicillin allergy

Faoud Ishmael, MD, PhD, Mount Nittany Physician Group Allergy & Immunology

Since the early 1940s, penicillin – a group of antibiotics that attack a range of bacteria – has been widely prescribed by doctors for the treatment of many common, as well as, more serious infections. The first line of treatment for many infections, penicillin works by interfering with bacteria cell walls and is so commonly used, in fact, that most Americans will have had at least one course of the drug by the time they are adults.

Just the facts
Simply put, the discovery and manufacturing of penicillin changed the face of medicine. And while these drugs have saved millions of lives over the years, many people don’t receive the benefits of this treatment because of a penicillin allergy on their medical record. In fact, around 10 percent of the U.S. population (30 million people) has an allergy to penicillin listed in their medical records, when in actuality, less than one percent of people are dangerously allergic to the drug. Many people with a documented penicillin allergy have never actually had the condition.

A true penicillin allergy is an abnormal reaction of your immune system to the drug. Common signs and symptoms of the allergy include hives, rash and itching, with the most severe reaction including anaphylaxis, a life-threatening condition that affects multiple body systems.

Considering the fact that less than one percent of the population has a true penicillin allergy, and that those who do will naturally lose the allergy over a period of five to 10 years, more than 90 percent of people are needlessly avoiding the use of penicillins.

There’s a test for that
So how do you know if you have a true penicillin allergy? Sensitive testing is available that allows allergy specialists to determine whether it’s safe for individuals to use penicillin. Such testing is incredibly important for a number of reasons.

  • Second-line antibiotics may not work as well. These medicines are used when the first-line therapy (or preferred treatment) is not able to be used because of allergy, side effects, or lack of availability.
  • Different antibiotics may be associated with more side effects. Those side effects include, but are not limited to nausea, vomiting, diarrhea, stomach pain, headache and rash. Some antibiotics may produce more serious side effects like abnormal heart rhythm or rupture of tendons.
  • People who are admitted to the hospital with a listing of a penicillin allergy have worse outcomes. These outcomes can include longer hospital stays and even higher risk of death.
  • Patients with a listing of penicillin allergy are also more likely to have antibiotic resistant bacteria. These bacteria can include methicillin-resistant Staphylococcus aureus (MRSA), Clostridium difficile (C. Diff), and Vancomycin-resistant enterococcus (VRE), and stems, in part, from using different antibiotics that are broad spectrum or not as effective.

It’s important to remember that while antibiotics such as penicillin aren’t always the answer, antibiotics can save lives and when a patient truly needs them, the benefits of the drug usually outweigh the risks of potential side effects.

To learn more about penicillin allergy and other healthy living topics, visit To schedule an appointment, call 814.278.4688, or visit

Faoud Ishmael, MD, PhD, is a board certified allergy and immunology physician with Mount Nittany Physician Group Allergy & Immunology, and offers particular expertise in allergy management and testing, including testing for allergies related to foods and medicines.