Think you are allergic to penicillin?
You might not be!
As an allergist, I have worked with countless patients who have thought they were allergic to penicillin but upon testing, we find out that it is not the case. In fact, 90 percent of people who report a penicillin allergy are found to be non-allergic.
Why is this?
Many patients were diagnosed with a penicillin allergy in early childhood because they got a rash after taking penicillin; but some of these rashes may have resulted from the infection itself, not from the penicillin. Others may have had an adverse reaction such as an upset stomach, but this isn’t a true allergy. In other instances, people truly were allergic to penicillin but outgrew the allergy over time.
Here is what you need to know about penicillin allergies, and why finding out whether you are actually allergic to this medication can help you and your doctor develop the right treatment plans for a bacterial infection.
What is penicillin? What is it used for?
Penicillin is part of the beta lactam group of antibiotics used to treat a variety of bacterial infections. Penicillin is often used to treat strep throat, ear infections, syphilis, urinary tract infections and pneumonia. It is also used to treat Group B strep in pregnant women.
What are symptoms of penicillin allergy?
Oftentimes, people who are allergic to penicillin develop a rash. The rash can develop after the first or second doses of penicillin, or it can first show up several days after completing the course of antibiotics.
Some people have an immediate allergic reaction to penicillin, which can include a rash, hives and swelling. Hives and swelling usually appear within an hour or less of taking penicillin. Sometimes, people have a severe allergic reaction known as anaphylaxis. Symptoms of anaphylaxis include difficulty breathing, dizziness, vomiting and loss of consciousness. Anaphylaxis is a medical emergency; call 911.
What conditions can mimic a penicillin allergy?
Some viruses cause a rash that may mimic a penicillin allergy. For example, the Epstein Barr virus – the virus that causes mononucleosis – when treated with amoxicillin (a type of penicillin) will cause a rash. This is not considered an allergy.
Another example is roseola, a common childhood virus that often causes a rash. Roseola also can lead to ear infections, which are usually treated with amoxicillin. If the child develops a rash, parents are often left wondering whether the rash was caused by roseola or amoxicillin. Parents should reach out to the child’s doctor to discuss whether they think the rash is caused by the virus or the drug. Allergy testing may be recommended depending on the child’s age. (Important note: Tummy troubles connected with penicillin are not signs of an allergy but are instead a side effect of many antibiotics.)
Why is knowing whether you are allergic to penicillin important?
Research has shown that patients with a recorded history of a penicillin allergy are usually prescribed non-penicillin antibiotics and have worse health outcomes. A study published in the Journal of Hospital Infection, for example, found that hospital patients with penicillin allergy records had longer hospital stays and increased antibiotic cost compared to those who did not have a recorded penicillin allergy. If a patient isn’t truly allergic to penicillin, that patient can be treated with lower-cost antibiotics and may have a shorter hospital stay.
We also know that patients labeled with a penicillin allergy often are prescribed broad-spectrum antibiotics instead, and these may not be as effective as penicillin. The infection may take longer to treat.
How does penicillin allergy testing work?
When I meet with patients in the office, I first go over medical history, including any recent illnesses and the drug reactions. Sometimes, I am able to determine from this history if penicillin allergy was misdiagnosed.
In other cases, we discuss allergy testing. One type of test is a skin test, where we prick the skin with different components of penicillin in the forearm. If the results are negative, we continue with an intradermal test, where we place a small amount of penicillin under the skin. If that is negative, then we may do a penicillin oral challenge. During the challenge, the patient takes a amoxicillin and is monitored for one hour for an allergic reaction. If there is no allergic reaction, we conclude that the patient is not allergic to penicillin.
Research shows that approximately 10 percent of patients report an allergy to penicillin, but with testing, we find that less than 1 percent of people really are allergic!
Who should be tested for penicillin allergy?
If you ever have been told you are allergic to penicillin, I suggest talking to your doctor about allergy testing. Given that so many people are mislabeled and given that so many people outgrow penicillin allergies, it’s often worth the while to find out for sure.
I also recommend that people who think they are allergic to penicillin and are planning to become pregnant be tested. Group B streptococcus is a type of bacteria that can be transmitted from pregnant woman to baby at the time of delivery. Women can be tested for Group B strep bacteria during pregnancy. If the test comes back positive, the woman can be treated with penicillin. There are alternative antibiotics that can be used if the pregnant woman is allergic to penicillin.
It’s also a good idea for people with a history of many antibiotic allergies and for people with a history of many different bacterial infections to be tested for penicillin allergy.
What if I am truly allergic to penicillin?
If you are among the 1 percent of people who are truly allergic to penicillin, you can still be treated with broad-spectrum antibiotics, in most cases.
Sometimes, treating an infection with penicillin is required. In these instances, an allergist will desensitize the patient to penicillin by giving very small amounts of the medication over several hours, essentially tricking the body into tolerating the medication. This is not a long-term solution to penicillin allergy – it does not “cure” the allergy – but it does enable patients to get the medication they need. If the patient needs penicillin in the future, the desensitization process will need to be repeated.
Can I outgrow a penicillin allergy?
Yes! In fact, outgrowing a penicillin allergy is very common. We don’t know why this happens but generally, most people who are diagnosed as allergic to penicillin are found to be non-allergic especially after 10 years or more.
Bottom line: Finding out whether you are truly allergic to penicillin can be helpful to you and your doctor. If you have reason to believe you are allergic, reach out to your physician to see if allergy testing is appropriate for you.