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Background Data on the diagnostic properties of direct oral challenges without the use of skin tests in children with suspected amoxicillin allergy are sparse. Objective Assess the use of direct oral challenges. Methods A cohort study was conducted between March 2013 and March 2020, in Montreal and Winnipeg. All children referred with reported history of benign reactions (ie, limited to the skin with no mucosal lesions and no vesicles) to amoxicillin were recruited and a 2-step graded oral challenge (GOC) was conducted. Data were collected on demographic characteristics, clinical characteristics, and comorbidities. Eligible children were followed to assess reactions to subsequent use of amoxicillin and to assess the safety of cephalexin use in children with a positive GOC. Results Among 1914 children recruited, 1811 (94.6%) tolerated the GOC, 42 (2.2%) developed mild immediate reactions, and 61 (3.2%) developed mild nonimmediate reactions. Among 265 participants who had a negative GOC and reused amoxicillin, 226 (85.3%) reported tolerance and 39 (14.7%) had mild cutaneous reactions. Chronic urticaria (adjusted odds ratio [aOR], 1.16; 95% CI, 1.09-1.23) and an index reaction occurring within 5 minutes of exposure (aOR, 1.09; 95% CI, 1.04-1.14) were associated with immediate reactions during the GOC. Symptoms lasting longer than 7 days (aOR, 1.05; 95% CI, 1.02-1.09) and parental drug hypersensitivity (aOR, 1.04; 95% CI, 1.03-1.06) were associated with nonimmediate reactions. Among those reacting to the GOC, 12.5% reacted with mild cutaneous reactions to cephalexin challenge. Conclusions Direct GOCs are an accurate and safe confirmatory to establish true hypersensitivity among children reporting benign reactions to amoxicillin.

Background Serum sickness–like reactions (SSLRs) are defined by the presence of rash (primarily urticaria) and joint complaints (arthralgia/arthritis) that are believed to occur due to a non–IgE-mediated response to medications. However, similar reactions can occur due to viral infections, and it can be difficult to distinguish between the two. This may lead to unnecessary avoidance of the culprit antibiotic. Objective We aimed to evaluate children presenting with suspected SSLRs through a graded oral challenge (GOC). Methods All children referred to the Montreal Children's Hospital for potential antibiotic allergy (β-lactam or other antibiotics) and a clinical presentation compatible with SSLR were recruited for the study between March 2013 and February 2020. A standardized survey with questions on treatment, symptoms, and associated factors was completed, and a GOC (10% and subsequently 90% of the oral antibiotic dose) was conducted. Patients with a negative GOC were contacted annually to query on subsequent antibiotic use. Results Among 75 patients presenting with suspected SSLRs, the median age was 2.0 years and 46.7% were males. Most reactions were attributed to amoxicillin. Among the 75 patients, 2.7% reacted immediately (within 1 hour) to a GOC and 4.0% had a nonimmediate reaction. Of the 43 patients successfully contacted, 20 reported subsequent culprit antibiotic use of whom 25.0% had a subsequent mild reaction (macular/papular rash). Conclusions This is the first and largest pediatric study to assess SSLR using a GOC. Our findings suggest that using a GOC is safe and appropriate for differentiating between β-lactam-induced SSLR and viral exanthem in this population.