allergies to penicillin antibiotic

Penicillin Allergies

Penicillin is an effective and widely used antibiotic. However, it’s a common drug that causes allergic reactions. Drug allergies are common, mostly in adults. This allergy causes the immune system to overreact and create antibodies when exposed to penicillin.

Some people experience an allergic reaction to penicillin the first time it’s taken. Other people won’t experience a reaction until they’re exposed multiple times. The next time someone with an allergy takes penicillin, their body will create antibodies. It’s this overreaction that allergy symptoms occur.

Some research suggests even a tiny amount of the drug can trigger an allergic reaction to those who are susceptible. Sometimes food contains traces of penicillin that can cause these reactions.

The body creates a type 1, immunoglobulin (IgE) reaction when allergic to penicillin. There are multiple drug allergies common in adults. These drugs include:

  • Penicillin
  • Ibuprofen
  • Naproxen
  • Aspirin
  • Chemo drugs
  • Anti-seizure drugs
  • Anti-HIV drugs
  • Insulin

Allergic reactions to drugs are different from the drug’s side effects. It’s also something different from drug toxicity caused by overdoses. Allergies are an entirely different issue.

penicillin allergies

Symptoms of Penicillin Allergies

Penicillin and other drug allergies can cause a variety of symptoms. These symptoms can range from mild to life-threatening anaphylaxis. The most common symptoms include:

  • Itchy rashes
  • Hives (urticaria)
  • Fever
  • Shortness of breath
  • Wheezing
  • Stuffy, runny nose
  • Itchy, swollen, and watery eyes

Life-threatening allergies are rare but can develop from drug allergies, especially in adults. Symptoms of anaphylaxis include:

  • Severe trouble breathing
  • Tightening and swelling of the airways
  • Swelling of the throat
  • Abdominal cramps
  • Vomiting
  • Diarrhea
  • Sudden drop in blood pressure
  • Rapid pulse
  • Seizure
  • Loss of consciousness

These symptoms required a 911 call, as emergency treatment is needed.

Penicillin Allergies in the US

According to the Centre for Disease Control and Prevention (CDC), about 10% of Americans report allergic reactions to penicillin class antibiotics. However, only about 1% have a true allergy with IgE mediated reactions. Furthermore, the majority (about 80%) lose sensitivity to the drug after ten years.

There are alternative antibiotics people with true penicillin allergies can take. They can use broad-spectrum antibiotics. However, there is a risk of antibiotic resistance. So, having a proper allergy diagnosis to penicillin is important.

doctor in white coat answering questions about penicillin allergies

Penicillin Allergies Q&A

Below, we answer the most commonly asked questions about penicillin allergies.

Can those with a true penicillin allergy take cephalosporins as an alternative?

A common concern people have is that they can’t take cephalosporin antibiotics if they have a penicillin allergy. They should discuss alternatives with their doctor.

The CDC suggests the newer generation of cephalosporins is safe to use if you have a penicillin allergy. However, the treating physician will review the medical history and evaluate if these drugs could be prescribed.

What tests show a true allergy to penicillin?

The doctor will take a detailed history and physical examination to determine if you have a penicillin allergy. They’ll ask about what kind of reaction developed, how long ago did the reaction occur and how was it managed.

In the case of true IgE-mediated allergy, the reaction occurs within an hour of taking the drug. Skin becomes itchy, with multiple pink raised areas – called hives. There may be swelling of some parts of the body, like the abdomen, face, or throat without hives. There may also be wheezing and shortness of breath. The doctor will also ask if there is a history of anaphylaxis and the need of taking epinephrine shots.

Based on your personal medical history and physical examination, your doctor may perform more tests. This includes a penicillin skin test and challenge doses for an accurate diagnosis.

How is are penicillin allergies managed?

Prevention is the best way to manage penicillin allergies. Those with allergies should avoid the drug and inform healthcare professionals of the allergy. It is important to have all allergies documented on your medical record.

To treat allergic reactions to penicillin, people take antihistamines and corticosteroids. These are generally available over-the-counter.

If anaphylaxis occurs, use an epinephrine shot. Those with a history of anaphylaxis should have an epinephrine kit for emergencies. Some cases may require multiple epinephrine shots.

Similar to seasonal allergies, drug allergies may improve with drug desensitization. During this treatment, a person will receive tiny doses of the drug that causes allergies. A doctor will gradually increase the dose over several hours or days. The treatment will continue if no allergic reaction takes place.


While penicillin is one of the most common drugs people are allergic to, true allergies to it are not common. Only about 10% of the population has experienced an allergic reaction, but do not have an allergy.

If you are truly allergic to penicillin, it’s important to avoid the drug. Let your doctors know of your allergy to the medication too.

You can take allergy medication to treat symptoms. A doctor may also suggest going for immunotherapy treatments.

Your email address will not be published. Required fields are marked *