Allergy test outcomes in patients self-reported as having penicillin allergy: Two-year experience

Background

Penicillin allergy is associated with increased antibiotic resistance and health care costs. However, most patients with self-reported penicillin allergy are not truly allergic.

Objective

To summarize our experience with allergy tests in patients with a history of penicillin allergy and to compare them with the results of other groups.

Methods

We retrospectively reviewed all patients with a suspected clinical history of penicillin allergy referred to the Drug Allergy Unit at University College London Hospital between March 2013 and June 2015.

Results

In total, 84 patients were reviewed. The index drugs included: unidentified penicillin (n = 44), amoxicillin (n = 17), amoxicillin–clavulanic acid (n = 13), flucloxacillin (n = 4), and other penicillins (ampicillin, benzylpenicillin, piperacillin-tazobactam; n = 7). Allergy diagnoses were confirmed in 24 patients (28.6%) (16 to penicillin, 3 to flucloxacillin, 5 to clavulanic acid). Twenty-two patients (91.7%) had allergy diagnosed by positive skin test results. Two patients (8.3%) developed IgE-mediated allergic symptoms during oral challenge (although the skin test results were negative). In vitro specific IgE test results for penicilloyl V, penicilloyl G, and amoxicilloyl were positive in 3 of 16 patients (18.8%). Moreover, reactions to cefuroxime were observed in 3 of 15 patients with penicillin allergy (20%). Selective clavulanic acid and flucloxacillin responders tolerated amoxicillin challenge. The interval between the index reaction and evaluation was shorter (P < .001), and the proportion of patients who could recall the name of the culprit drug was higher (P = .009) in the allergic group. Furthermore, histories of anaphylaxis (33.3%), urticaria, and/or angioedema (58.3%) were more common in the allergic group. Unspecified rashes (35.0%) and nonspecific symptoms (28.3%) predominated in the nonallergic group.

Conclusion

Only 28.6% of patients with self-reported penicillin allergy were confirmed to be allergic. Importantly, when the index drug is amoxicillin–clavulanic acid or flucloxacillin, the patients may tolerate amoxicillin.