Penicillin Allergy: Why You Should Be Evaluated

Penicillin is one of the most common medication allergies reported by patients. Here’s what you should know.

About 10 percent of the population list penicillin or a penicillin derivative as an allergy. However, 95 percent of these patients are not actually allergic and can have this medication removed from their allergy list after evaluation by an allergist.

What is a penicillin antibiotic?

Penicillin antibiotics are used to treat bacterial infections such as ear infections, strep throat, and sinus infections. Penicillin antibiotics include penicillin itself, as well as several derivatives such as amoxicillin and Augmentin. These antibiotics are very often the first line, most effective, and safest medications to use, but they cannot be used in patients with any of the penicillins listed as an allergy on their medical records.

What is the benefit of penicillin allergy evaluation?

An inaccurate penicillin allergy label can be quite costly and may result in the use of less effective antibiotics for treatment.

“Having a mislabeled penicillin allergy on your medical chart can cause problems,” says Jason Cascio, MD, PhD, of McFarland Clinic Allergy & Immunology. “Having a penicillin allergy label leads to the use of less effective and more costly antibiotics, increased risk of developing multi-drug resistant infections, increased risk of surgical site infections, and increased all-cause mortality.”

Fortunately, Dr. Cascio says that the vast majority of people with a penicillin allergy listed in their charts are not actually allergic to penicillin and can tolerate the antibiotic.

“Penicillin allergy is commonly diagnosed early in childhood, often because of a rash,” says Dr. Cascio. “However, more often than not the rash was caused by the illness that they had at the time, but the antibiotic incorrectly took the blame and was wrongly listed as an allergic reaction.”

In addition, even patients with a history of a true allergic reaction to penicillin will outgrow the allergy with time.

“Supposing someone had a true allergic reaction to a penicillin antibiotic, we know that after 5 years, 50 percent of people will lose that allergy. After 10 years, 80 to 90 percent of people will lose that allergy. And after 20 years, nearly 100 percent will have lost that allergy,” says Dr. Cascio.

Dr. Cascio notes that allergy testing is beneficial for the entire penicillin antibiotic class, which includes penicillin, amoxicillin, ampicillin, nafcillin, Augmentin (amoxicillin/clavulanate), Unasyn (ampicillin/sulbactam), and Zosyn (piperacillin/tazobactam), among others.

How do I know if I am allergic to penicillin or not?

Allergy testing can determine if someone is allergic to a drug or antibiotic such as penicillin. Anyone with a history of an allergic reaction to penicillin or any antibiotic should be evaluated. 

Testing can be done in-office and takes about one hour. The results are determined during the visit.