Penicillin allergy is the most commonly reported drug allergy in the United States. The overall prevalence is about 10% in the general population. After proper diagnosis and evaluation, 80% to 90% of people with self-reported penicillin allergy are actually not allergic. Additionally, even in those select patients with true allergy to penicillin, the frequency of positive results on skin testing decreases by 10% per year of avoidance. In other words, if you had a true allergy to penicillin and avoided it for 10 years, there’s an 80% chance you are no longer allergic.
Unlike allergic rhinitis, asthma, or eczema, there is no predictable pattern to inheritance of penicillin allergy. You do not need to avoid penicillin if a family member is allergic to penicillin or drugs in the penicillin family.
What is penicillin?
It was first discovered by Alexander Fleming in 1928 and it is widely prescribed today to treat many infections, such as strep throat, sinusitis, and pneumonia. It belongs to a family of antibiotics known as beta-lactams. Other antibiotics in this same category include Penicillin G, nafcillin, oxacillin, dicloxacillin, ampicillin, amoxicillin, carbenicillin, ticarcillin, and piperacillin. If you are allergic to penicillin, you should be avoiding these other medications as well.
Adverse reactions to penicillin
Non-allergic adverse reactions are much more common than an allergic reaction to penicillin. Common symptoms include nausea, upset stomach and diarrhea.
Allergic reactions to penicillin
Just like with any type of allergy, at first exposure, the body may be sensitized, but typically no allergic reaction occurs. Upon re-exposure, in a previous sensitized person, an immediate allergic reaction can occur quickly, anywhere from a few minutes of receiving penicillin up to a few hours.
Mild to moderate allergic reactions occur in about 1-5% of people taking the medication. Symptoms may include itchy hives and swelling of the face and/or extremities. Treatment usually involves antihistamines, oral or injected corticosteroid, and avoidance of penicillin.
Severe reactions, such as anaphylaxis, are not common, but they can be life-threatening and can include swelling of the throat, lips and face, chest tightness and/or wheezing, nausea and vomiting, lightheadedness and passing out from low blood pressure. Treatment involves epinephrine. If left untreated, anaphylaxis can lead to shock, heart failure, and death.
Penicillin allergy testing and diagnosis
Testing is important for anyone who has had a suspected allergy to penicillin or a penicillin-related antibiotic such as amoxicillin or others.
There are two main components in penicillin that can cause allergy. The major determinants include benzlypenicilloyl, or PRE-PEN. The minor determinants include penicilloate, penilloate and penicillin G. More than 90% of allergic reactions occur with PRE-PEN.
Diagnosis for penicillin allergy involves performing skin prick testing with PRE-PEN and Penicillin G. A small amount of the components are dropped onto the arm and the skin is pricked with a plastic pricking device. If there is no reaction, further testing involves an intradermal skin test where the penicillin components are injected underneath the skin with a needle. If no reaction, a dose of penicillin is administered orally in our office under supervision. After passing this test, penicillin is given twice a day at home for 7 days to rule-out any delayed reactions. If this is tolerated, you are not allergic to penicillin and the penicillin allergy label may be removed from your medical records.
A positive skin reaction to either skin prick testing or intradermal testing indicates allergy. People with a positive test should avoid penicillin and penicillin related medications. In the case of infections, different antibiotics would be recommended.
In certain situations, penicillin or penicillin related antibiotics may be the only treatment of choice for an infection. Penicillin desensitization is a procedure that induces drug tolerance and temporarily allows a penicillin allergic patient to take penicillin safely. This procedure involves administering small amounts penicillin with increasing doses at regular intervals until a full dose is reached. The patient will be able to tolerate the medication if the medication is continued. Once the medication is stopped, a person is at risk for a sudden allergic reaction. A repeat desensitization procedure is required if the same medication is needed again. This procedure can be done in our office or hospital setting.
What is the next step?
If you think you might be allergic or have penicillin listed as one of your medication allergies, it is best to come see us at North Texas Allergy and Asthma Center for further evaluation and proper diagnosis. Our allergists are board certified in both pediatric and adult allergy and immune system conditions. We will work together with you to create a good treatment plan.
SHIKHA MANE, MD
Board Certified Allergist