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Are You Actually Allergic to Penicillin? How to Find Out

If you or your child has had strep throat, an ear infection or a urinary tract infection, there’s a good chance your provider sent you to the pharmacy with a prescription for penicillin. Penicillin is an antibiotic, which means it kills bacteria. It has saved countless lives since it was discovered almost 100 years ago. 

However, some people are allergic to penicillin. Their immune system flags penicillin (or related antibiotics) as harmful. Within minutes, they could have:

  • Skin reactions: Rash, hives, itching, redness or blistering
  • Respiratory symptoms: Wheezing, shortness of breath, coughing or nasal congestion
  • Digestive symptoms: Nausea, vomiting, diarrhea or abdominal pain
  • Swelling: Swelling of the face, lips, tongue or throat
  • Anaphylaxis: A severe, life-threatening allergic reaction with difficulty breathing, rapid drop in blood pressure, loss of consciousness and shock

So penicillin allergies are something to watch for. But a lot of people who think they are allergic to penicillin aren’t.

“Overall, less than 1% of people are allergic to penicillin,” said Puneet Shroff, MD, an allergist with Banner – University Medicine. “But about 10% of people think they have a penicillin allergy.”

Why do so many people think they’re allergic to penicillin? These reasons might play a role:

  • In childhood, they had a rash caused by the condition they were treating and were told they had a penicillin allergy. They were never properly evaluated.
  • They have a parent with a penicillin allergy, so they believe they have it as well.
  • They had an allergy, but it has likely gone away over time. 
  • They had side effects like a rash, upset stomach or diarrhea, which are common when taking antibiotics and not usually signs of an allergy.

Why not just take another antibiotic?

There are more than 100 different types of antibiotics. What’s the big deal about penicillin? You might think you should just avoid penicillin, to be on the safe side. 

Penicillin is one of the antibiotics health care providers turn to the most. It works against lots of different types of bacteria. “Penicillin is a safe, cost-effective antibiotic,” Dr. Shroff said.

If you rule out penicillin, you also need to avoid a group of antibiotics in the same drug family, including amoxicillin (Augmentin). That means:

  • You might need an antibiotic that’s less effective, more expensive or has more side effects. The side effects could be worse than what you experience with penicillin.
  • You might not get better as quickly.
  • You might need more than one antibiotic to treat your condition. 
  • You’ll have to consider other antibiotics for surgery, dental procedures or other medical care. 
  • You’ll need to watch for interactions between alternatives to penicillin and other drugs you take. They could interact differently than they do with penicillin.

Alternatives to penicillin can also increase health care costs, play a role in antibiotic resistance and contribute to infections that spread in hospitals.

How can you find out if you’re really allergic to penicillin?

“First, take a thorough history with your primary care provider. Go through any medical records you have,” Dr. Shroff said. It can be helpful to answer these questions:

  • When did a reaction take place?
  • What happened, exactly? What symptoms can you report?
  • What else was going on? Why were you being treated with penicillin?

“If your provider thinks you may have a penicillin allergy, they may refer you to an allergist,” Dr. Shroff said. “Penicillin allergy testing is very safe, though many people don’t need it if their risk of allergy is low or negligible.”

Depending on your history, symptoms and risk factors, your provider may recommend one of these options to test for a penicillin allergy:

  • Skin prick test: A small amount of penicillin extract is placed on your skin, usually on the forearm or back. Then, a provider pricks your skin with a tiny needle to put the penicillin under it. If you're allergic to penicillin, you’ll have a red bump there within 15 to 20 minutes.
  • Intradermal test: This test involves injecting a small amount of penicillin extract under the skin’s surface with a fine needle. It is more sensitive than the skin prick test and might be used if the skin prick test results aren’t clear.
  • Patch test: Small amounts of penicillin are applied to patches placed on your skin to see if you develop an allergic reaction. Patch testing isn’t that common for penicillin allergies.
  • Blood tests: Tests such as specific IgE (immunoglobulin E) tests measure the levels of penicillin-specific antibodies in the blood. They can provide information about your immune response to penicillin but aren’t as sensitive as skin tests.

If these tests don’t show signs of a penicillin allergy, you may move on to an oral challenge. That’s where you take several small doses of penicillin by mouth, and you are monitored for the next hour or two for any reaction. You can usually do the oral test during the same doctor’s visit as the skin test.

If these tests don’t show signs of a penicillin allergy, your doctor will likely decide that you don’t have one and recommend taking it off your medical record. That way, if you need treatment with penicillin or a related drug, you’ll be able to take it.

If you’ve been told you have a penicillin allergy, it’s a good idea to look into testing when you’re healthy. “Once you’re sick and might need a penicillin product, testing may not be appropriate,” Dr. Shroff said.

What if you have a penicillin allergy?

It’s good to find out that you aren’t allergic to penicillin. But what if testing shows that you are? There are still lots of antibiotics that can work for you. If you need one, you can talk to your provider about what might work best, with the lowest risk of side effects.

Options include: 

  • Macrolides such as azithromycin and clarithromycin
  • Fluoroquinolones such as levofloxacin and ciprofloxacin
  • Tetracyclines such as doxycycline and minocycline
  • Cephalosporins such as cephalexin and others

The bottom line

Many people think they have a penicillin allergy, but that might not be the case. If you’re not sure if you’re actually allergic to penicillin, talk to your health care provider about testing. Penicillin is an effective, inexpensive drug that’s safe for most people and might be a better choice in a lot of situations. So it’s good to find out if it’s an option for you.

To learn more about penicillin allergies and antibiotic options, reach out to an expert at Banner Health.

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