The truth about penicillin allergies

Penicillin and related drugs such as amoxicillin are among the most commonly prescribed antibiotics in the U.S. — and are thought to be among the most common drug allergies. In fact, 10% of all patients report having had an allergic reaction to the antibiotic widely used to treat bacterial infections, such as sinus infections, dental abscesses, urinary tract infections and strep throat.

However, according to experts at the Centers for Disease Control and Prevention (CDC), less than 1% of people are truly allergic to penicillin, and of that 1%, close to 80% lose their sensitivity after 10 years.

“People can be diagnosed with a penicillin allergy at any age, but the most common is usually in childhood when being treated for an infection,” says Dr. Bryn Salt, an allergist and immunologist with Sharp Rees-Stealy Medical Group. “However, over 95% of people who have been diagnosed with a penicillin allergy can take it safely later in life. We suspect that some are misdiagnosed and others may outgrow the allergy over time.”

Symptoms of a penicillin allergy
According to Dr. Salt, an authentic penicillin allergy could cause a variety of reactions, which often occur within an hour of taking the drug. These symptoms include:

• Hives

• Swelling

• Difficulty breathing

• Nausea, vomiting or diarrhea

• Change in pulse (weak or rapid)

• Seizures

• Shock

• Loss of consciousness

“The most common reaction people have to penicillin is a rash, which most of the time is not an allergy at all,” Dr. Salt says. “The rash may be due to the underlying infection or a delayed hypersensitivity reaction, neither of which is life-threatening.”

Two kinds of drug allergy tests
If you have been told you have a penicillin allergy or believe you might have an allergy due to a prior reaction to taking penicillin, talk to your doctor. You can be tested for a true allergy using either skin testing or a direct challenge to the drug.

A skin test consists of a skin prick and intradermal test, done 15 minutes apart. For the skin prick test, a small amount of diluted allergen is applied to the skin using a small plastic device that punctures the skin. The intradermal test includes injecting a small amount of diluted allergen under the surface of the skin. In both tests, doctors watch for a skin reaction, which can indicate an allergy. A drug challenge involves giving the patient a dose of amoxicillin and observing for one hour after to assess for allergy.

“It is important to be tested because it can make a big difference in a patient’s medical care over time,” Dr. Salt says. “Penicillin drugs are often the most effective drugs for many common infections and tend to have fewer side effects than other antibiotics. They also are less expensive, and the use of penicillin rather than other antibiotics helps to reduce antibiotic resistance.”

If a penicillin allergy is confirmed, it is important that you notify all health care providers — including your dentist — and confirm that your allergy is noted in your medical records. You might also consider wearing a medical alert bracelet with your allergy information and carrying an epinephrine auto-injector, commonly known as an EpiPen, in case of anaphylaxis.