Penicillin intolerances are common, reported by approximately 1 in 10 patients, though for many, a true penicillin allergy may not exist, or the allergy may resolve over time.1 Those with the allergy may also have an allergy to other antibiotics, primarily those in the beta-lactams class, which includes cephalosporins and carbapenems.2,3 It is suspected that having an allergy documented to a first-line antibiotic can lead to higher costs and antibiotic resistance as second-line antibiotics are used.2
To understand the relationship between having an allergy to penicillins and the presence of additional antibiotic class allergies, we studied 1,663,701 patients prescribed or administered penicillin and an additional antibiotic class. Patients were required to have at least one non-antibiotic allergy documented or an allergy documentation of no known allergies prior to receiving penicillin or in the year that followed. The 31,319 patients with a documented penicillin allergy were matched 1:4 with patients without a documented penicillin allergy based on antibiotic class, sex, race and ethnicity. We further adjusted for factors such as number of documented allergies, race, ethnicity, and age.
We found that patients who had a penicillin allergy were more likely to have additional antibiotic allergies than those without a penicillin allergy, as seen in Figure 1. Specifically, those with a penicillin allergy were 308% more likely to have an allergy to cephalosporins, 305% more likely to have an allergy to carbapenems, and 234% more likely to have an allergy to macrolides. Among all the studied antibiotic classes, patients had the least increased (152%) likelihood of having an aminoglycoside allergy. Of note, carbapenem antibiotics are less frequently used than other studied antibiotics as they are typically prescribed for less common infections with multidrug-resistant organisms, resulting in a smaller population with potential exposure.4
