Health Education

Do you really have a penicillin allergy? Check again.

Avatar By | November 11, 2019
Medically reviewed by Raymond Zakhari, DNP, EdM, NP-BC

A few days after my daughter started taking her first antibiotic, at around a year old, she broke out in a rash. I called her doctor immediately. The pediatrician’s office told me to stop the medication. She’s been branded with a penicillin allergy ever since.

It didn’t seem like a big deal at first. I like to let illnesses run their course without antibiotics, whenever possible. For a few years, she never needed a prescription. But then, she was diagnosed with an autoimmune condition and put on immunosuppressant drugs. Suddenly, she required antibiotics to kick any little illness.

When you can’t take penicillin, the antibiotic options very quickly narrow. Several of those options made my daughter sick. I had to fight to get her to take them and take lots of trips to the bathroom with her after she did.

When a new physician specializing in penicillin allergy joined her medical team, her pediatrician was quick to sign her up for testing.

Is it a true penicillin allergy?

American Academy of Pediatrics spokesperson John Kelso, MD, specializes in allergies and immunology. He recently told The Checkup that while approximately 10% of children will be labeled as being allergic to penicillin, “It turns out about 95% of them are not allergic at all.”

He said this happens for several reasons:

  1. It’s not uncommon for children to develop a secondary rash in reaction to the initial infection that required treatment in the first place, as opposed to developing a penicillin rash in reaction to the medication.
  2. There is something called an amoxicillin rash that is a fairly common reaction to amoxicillin, but is not actually an allergic reaction, and isn’t especially dangerous, according to Dr. Kelso.
  3. Some kids do have a true allergic reaction, but they outgrow it in the years that follow.

Dr. Kelso says a lot of what is labeled as a penicillin allergy is exactly what my daughter experienced: a rash that develops a few days into treatment, occurs the first time penicillin is given, is relatively minor, and isn’t hive-like in nature.

Signs of a true penicillin allergy

He explained that a true allergic reaction doesn’t typically develop the first time a medication is given. This is because, “a penicillin allergy, like any allergy, requires some prior exposure. Nobody is born allergic to anything. We think you cannot develop an allergy during your first exposure to penicillin.”

For this reason, he said a true penicillin reaction will usually:

  • Develop with subsequent prescriptions of penicillin, not with the first prescription
  • Appear relatively soon after the first dose with subsequent prescriptions, not multiple days into the treatment
  • Present as raised hives, most often

The benefits of penicillin allergy testing

Allergist and immunologist Kathleen Dass, MD, has cleared hundreds of people of what they thought were penicillin allergies. Recent research, published in Open Forum Infectious Diseases, found that 98 out of 100 patients who had a penicillin allergy in their charts were not actually allergic.

A lot of parents, and adults with their own penicillin allergy designation, may not fully understand the benefits of testing. But Dr. Dass says there are several reasons to be tested for a penicillin allergy, such as:

  • Being able to receive the best and most appropriate antibiotic you need
  • Decreasing your risk of antibiotic resistance and for antibiotic-associated diarrhea
  • Decreasing healthcare costs
  • Receiving clearance to take cephalosporin and carbapenem antibiotics

In most cases, Dr. Dass recommends waiting 10 years after a presumed reaction to have testing done, “unless there are no alternative antibiotics that can be used.” In our case, it made sense to have testing done earlier. But most families are probably safe to wait.

What does penicillin allergy testing include?

Dr. Dass says that testing generally starts with an allergist taking your history and finding out more about the initial diagnosis of a penicillin allergy. “Any patient with a documented history of penicillin allergy is a candidate for penicillin testing,” Dr. Dass explains. “However, [your physician] will only proceed if it is safe to do so.”

Allergy skin tests

For my daughter, the next phase of testing included four markings being made on her skin to designate:

  • A histamine
  • Saline
  • Two known penicillin reactants

Next to each of these markings, tiny droplets of each substance were simply placed on, and rubbed into, her skin. We were then told to wait 15 minutes to see if there was a reaction. There was not.

Skin prick testing

The next part of the testing is skin prick testing, according to Dr. Dass, “which is a prick to the skin that does not go deep and should not be painful.”

My daughter would disagree with that last statement, but then… she’s 6, and needles are scary. She calmed down within 30 seconds of the skin pricks.

Subcutaneous injections

When testing to the skin prick is negative, the next state of testing is subcutaneous injections.

In my daughter’s case, this part of the testing was skipped. Because of her negative reactions to the first two parts of testing, and because of the overall description of her initial reaction (a rash that wasn’t hive-like in nature and that developed a few days into her first course of penicillin), and because she was younger than most kids who typically have this testing done, the allergist doing her testing weighed the pros and cons and felt comfortable skipping additional needle trauma.

I, and my daughter, were both appreciative. But not all allergists may have the same level of comfort, and parents should always follow the advice of the allergist doing their child’s testing.

Oral testing

If a patient passes the subcutaneous injections, the next step is oral testing. “This means the patient will receive at least two doses of penicillin antibiotic, which is usually incrementally larger doses of penicillin,” according to Dr. Dass. “Patients are monitored frequently afterward, usually for one hour or longer.”

Over the course of that testing, my daughter had zero reaction. And Dr. Dass says, “If this is negative, then you are at no greater risk for having the allergy than anyone else!”

RELATED: When to allergy test your child

Removing the penicillin allergy

We removed my daughter’s penicillin allergy from her medical chart almost immediately after testing. It’s now one less thing we have to worry about when she develops infections.

Dr. Dass says all hope isn’t lost for those cases that are deemed too risky for testing, though. First, alternative antibiotics will be used. “If there is no alternative antibiotic, then a desensitization procedure occurs to achieve unresponsiveness to the drug. This includes starting with a very small dose of penicillin and giving incrementally higher doses of penicillin over hours or sometimes days.”

Obviously, this should only occur under the supervision of a physician.

Still, Dr. Dass concludes, “Evaluating for a penicillin allergy is safe, and it’s much easier to evaluate this allergy when you’re not sick rather than when you’re in a life-threatening situation in a hospital.”

She also wanted to make clear that while there is a common misconception that penicillin allergies are hereditary, that is not always the case. “If your parent had a life-threatening penicillin allergy, this does not mean you have a penicillin allergy.”

For our part, I am so glad we had testing done and that my daughter’s pediatrician now has a greater pool of antibiotics to choose from whenever she gets sick.

To find an allergist who can test in your area, use this link to search by zip code.