Risk stratification for outpatient penicillin allergy evaluations
Huebner, Emily Margarete
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OBJECTIVES: Penicillin allergies are the most commonly reported drug allergy. However, recent research has supported the concept that reported penicillin allergy does not equal true allergy. False penicillin allergies and associated alternative antibiotic use can result in inferior clinical outcomes. Determination of true versus self-reported allergy can be determined through skin testing to penicillin and oral challenge to amoxicillin. Penicillin allergy evaluations improve antibiotic utilization but penicillin skin testing (PST) requires more resources than oral amoxicillin challenge alone. Because amoxicillin challenge without preceding PST may be safe in low-risk patients, we assessed a risk stratification tool for outpatient penicillin allergy evaluations that stratify low-risk patients to receive amoxicillin challenge without prior skin testing. METHODS: The patient population was identified using the Massachusetts General Hospital Allergy Associates clinic schedule in EPIC from the beginning of January 2017 through the end of July 2018. Patients were classified into one of two evaluation methods based on allergy history, using the MGH Allergy Associates Outpatient Penicillin Allergy Pathway. Patients deemed low-risk were evaluated with direct 2-step oral amoxicillin challenge. Intermediate-risk patients were evaluated with PST and subsequent oral amoxicillin challenge. Skin testing (ST) was performed using epi-cutaneous prick tests with a major and minor determinate of penicillin, histamine (positive) and saline (negative) controls, followed by intradermal injections of the same reagents. ST was followed by one oral dose of 500mg amoxicillin. Direct oral challenge involved doses of 50mg of amoxicillin in the first step or 500mg of amoxicillin in the second step. These patients’ charts were retrospectively reviewed for information regarding the initial antibiotic allergic reaction, type of allergy testing administered, and outcomes of the outpatient allergy testing. Analysis was performed to assess and significant differences in patient characteristics, safety, and outcomes in patients given preceding skin testing or direct oral amoxicillin challenge. RESULTS: Overall, 509 eligible patients were reviewed. Four hundred twenty-six patients underwent PST with subsequent oral amoxicillin challenge. The remaining 83 patients received direct, two-step oral amoxicillin challenge. Across both groups, 43 adverse drug reactions (ADRs) were observed, 26 of which were considered hypersensitivity reactions (HSRs). The proportion of patients in each testing group that experienced ADRs was near equal, 8.5% of the skin tested group and 8.4% of the direct challenge group. One patient in each group had an HSR requiring treatment with epinephrine. Using multivariate logarithmic analysis to evaluate potential predictors for ADRs and HSRs, female sex was the only variable associated with significant increased odds for an ADR. There were no significant findings for increased odds for HSRs, including evaluation method with direct drug challenge. The proportion of patients considered to have a true penicillin allergy was similar in the two groups. DISCUSSION: PST is a vitally important aspect of antibiotic stewardship, especially when conducted before antibiotic treatment is required. Though the standard procedure is skin testing with penicillin, followed by oral amoxicillin challenge, direct oral challenges can be considered for appropriately selected low-risk patients presenting for penicillin allergy evaluation. PST is nonetheless advisable for patients with higher risk allergy histories, pregnant patients, and patients with tenuous cardiac or pulmonary status.