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Know The Facts About Penicillin Allergies

September 28 was National Penicillin Allergy Day. Penicillin is the most commonly reported drug allergy. Reactions from penicillin can range from mild to severe. Dr. Raghavendra Tirupathi, Medical Director of Keystone Infectious Diseases, wants to educate the public about penicillin allergies, and shares important information for those who have had past allergic reactions to penicillin or a related drug.

What is penicillin?

Penicillin was discovered by Alexander Fleming in 1928. Ninety years later, it is still one of the most important and commonly prescribed antibiotics. The penicillin family of antibiotics has more than 15 chemically related drugs, including penicillin, amoxicillin, amoxicillin-clavulanate, ampicillin, methicillin, and dicloxacillin that are given to treat many bacterial infections. A penicillin allergy is an abnormal reaction of your immune system to the antibiotic penicillin.

What causes a penicillin allergy?

A penicillin allergy occurs when your immune system mistakes the drug for a harmful substance. It happens when a body reacts to penicillin as if it were an infection instead of an antibiotic. Your immune system needs to be exposed to penicillin at least one time before it can develop sensitivity to it. If sensitivity does develop after your immune system mistakes it for a harmful substance, you will develop an antibody to the drug. Antibodies identify and counteract foreign objects such as bacteria and viruses that enter your body. The next time you take penicillin, these specific antibodies detect it and direct the immune system to attack the substance. There are chemicals that are released by this activity, and they cause the symptoms of an allergic reaction.

Are penicillin allergies common?  

About 10% of the population reports that they are allergic to penicillin. However, most of these patients (90% or more) may not actually be allergic. The majority of people lose their allergy to penicillin over time. Even those who reported a strong reaction in the past, such as anaphylaxis (a severe, potentially life-threatening allergic reaction) may lose their allergy.

Are penicillin allergies genetic?

There is no evidence of penicillin allergies being genetic. Just because a family member is allergic to penicillin or an antibiotic in the penicillin family, you do not need to be scared to take the medication.

What are some of the symptoms of a penicillin allergy?

There are several reactions that can occur immediately or shortly after (usually within one hour of) dosage. These include: hives (multiple raised pink/red areas of the skin that are intensely itchy), tongue, throat and face swelling, shortness of breath, wheezing, sensation of throat closure or choking, change in voice-quality, lightheadedness, racing of the heart, chest pain, a sense of impending doom, and/or loss of consciousness, nausea, vomiting, abdominal cramping and diarrhea.

Reactions that occur later can include a whole body rash similar to measles which occurs five to seven days after starting the antibiotic

What do patients who have a penicillin allergy need to know?

They should be sure that their penicillin allergy or other antibiotic allergy is accurately identified in their medical records. Please make sure the type of reaction is also documented clearly. If the allergy is severe, you should wear a medical alert bracelet that identifies your drug allergy. This information can ensure proper treatment in an emergency.

Why is it very important to identify and document penicillin allergies accurately?

Penicillin is the most commonly reported drug allergy. Patients who report penicillin allergies tend to receive more expensive and stronger antibiotics, which can lead to significant adverse effects and antibiotic resistance. By identifying patients who are not actually penicillin allergic, we can improve antibiotic prescribing methods and combat the risk of super-bugs like MRSA and C-Diff. Penicillin allergy testing is available and may be beneficial to your future health. 98% of hospitalized patients with a history of penicillin allergies have a negative result when tested.

Know the facts and get tested. Talk to your doctor about penicillin allergy testing.


This article contains general information only and should not be used as a substitute for professional diagnosis, treatment or care by a qualified health care provider.