Penicillin Allergy Testing in Antibiotic Stewardship

Clinicians should perform confirmatory allergy testing on patients with reported penicillin allergies as an important feature of antimicrobial stewardship, according to George Sakoulas MD, from the University of California San Diego School of Medicine, La Jolla, and colleagues.

“[C]onsistent data have emerged pointing toward possible shortcomings in clinical outcomes and medical care costs when utilizing non-beta-lactam antibiotics in patients with penicillin allergies,” the authors write in a recent study published online in Clinical Infectious Diseases.

Although an estimated 25 million Americans self-report penicillin allergy, up to 98% of these individuals are found to be non-allergic after penicillin allergy testing.

Nevertheless, because of their penicillin allergy label, these patients ultimately tend to receive different classes of antibiotics, as shown by one study in which up to 51% of vancomycin use was reported to have been as an alternative to penicillin in patients with a documented penicillin allergy; this can negatively affect treatment and health outcomes, the authors say.

Studies have shown, for example, that when compared to individuals without allergy, patients with a penicillin allergy label wait much longer to receive a first antibiotic dose and have significantly longer hospital stays. They also experience more infections due to Clostridium difficile, methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE). Researchers have suggested that increased use of vancomycin, clindamycin, and fluoroquinolone has increased patients’ risk of developing these infections.

Additionally, those with documented penicillin allergies have much greater odds of developing a surgical site infection or experiencing an adverse event.

These problems also affect health care costs, as demonstrated by data showing that a penicillin allergy label translated into an average excess cost of $1,145 to $4,254 per patient for outpatient and inpatient drug costs and inpatient hospitalizations.

Studies have shown that the useful antibacterial properties of beta-lactam antibiotics exceed what is understood about how these agents perform in standard bacteriological susceptibility testing. Unlike other antimicrobial classes, beta-lactams have adjunctive properties that modulate how bacteria interact with, and become vulnerable to, the innate immune system.

In particular, beta-lactams make MRSA more susceptible to the innate immune system, including antimicrobial peptides. Similarly, these agents have been shown to increase the susceptibility of VRE to cationic peptides and immune clearance.

By enhancing the killing of such organisms in this way, beta-lactams may improve how efficiently the body clears bacteremia, the authors suggest. “Patients who receive non-beta-lactam antibiotics in response to purported penicillin allergy may be missing out on these significant effects that enhance treatment or prevent infection,” they write.

Consequently, penicillin allergy testing can be an important and cost-effective component of a successful antimicrobial stewardship initiative, the authors stress.

“Although it is common for a patient or family member to declare a drug allergy, treating clinicians must verify the allergy by taking a thorough history and, if deemed necessary, test for a Type 1 reaction,” conclude Dr Sakoulas and colleagues. “Often, obtaining a thorough history by interviewing the patient has proven effective in removing the purported allergy from the patient’s medical profile.”

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.