ASK THE PHARMACIST
Penicillin Allergy in the ED: What Should I Do Next?
SAEM PULSE | JULY-AUGUST 2025
By Alicia Pycraft, PharmD, on behalf of the SAEM Academy of Emergency Medicine Pharmacists
24
Penicillin allergies are the most commonly reported drug allergies, with approximately 10% of patients worldwide claiming to be allergic. However, studies show that 95% of these individuals do not have an IgE-meditated hypersensitivity and can tolerate penicillins safely. In many cases, symptoms of viral illness—such as rash or fever—are misinterpreted as allergic reactions, leading to inaccurate labeling in childhood.
are often first-line therapies for many infections. Patients labeled as allergic are frequently prescribed second-line or broader-spectrum antibiotics, which contributes to antimicrobial resistance. Documented penicillin allergies have been associated with increased risks of healthcare-associated infections, surgical site infections, prolonged hospital stays, higher antibiotic costs, and increased readmission rates.
Mislabeling patients with penicillin allergies can significantly affect clinical outcomes, as beta-lactams
Although many patients are incorrectly labeled as allergic, penicillin remains the leading cause
of drug-induced anaphylaxis in the United States among those with true allergic reactions. Therefore, careful evaluation of reported penicillin allergies is essential to ensure safe and effective antimicrobial therapy.
Classification of Hypersensitivity Reactions
When evaluating a reported penicillin allergy, it is critical to distinguish low-risk histories from true immune-mediated hypersensitivity. Low-risk histories may include gastrointestinal upset, a family history of penicillin allergy, pruritus without rash, or remote, unknown