The correct answer is:

Observation

Educational Objective:

Discuss the differences between a type IV hypersensitivity reaction to amoxicillin and a benign "amoxicillin rash."

Key Points:

People often mistakenly think they are allergic to penicillin, even when they aren’t.

Explanation:

This is a diffuse erythematous macular rash seen after amoxicillin administration, especially if the patient has undiagnosed mononucleosis or another viral syndrome that is inadvertently treated with amoxicillin.

This so-called “amoxicillin rash” does not represent an allergic reaction and should not prevent patients from completing the current course or receiving penicillins in the future. It will resolve spontaneously in 7-10 days and does not require treatment. It will not recur except perhaps if a future viral infection is again inadvertently treated with amoxicillin.

The absence of pruritus and angioedema in a well appearing, afebrile child renders the diagnosis of “benign amoxicillin rash” more likely than “allergic reaction to amoxicillin” (especially in the context of a positive mono test). By contrast, the urticarial rash of an amoxicillin allergic reaction is pruritic and has angioedema (raised rash - see figures).

The "amoxicillin rash" was first noticed in the 1960s in children who were being treated with ampicillin for mono, according to the Journal of Pediatrics. The rash was reported to have developed in almost every child, between 80 and 100 percent of cases.

Figures:

Benign maculopapular reaction to amoxicillin in a well child without fever

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Urticaria with angioedema within the lesions

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