Making a rash diagnosis: amoxicillin therapy in infectious mononucleosis

The ampicillin analog, amoxicillin, can potentially produce the same hypersensitivity reaction as the ampicillin. The case of a patient treated with amoxicillin for a sore throat, who later presented with a rash, is reviewed. Infectious mononucleosis was considered and then supported by a positive mono spot. It would appear therefore that amoxicillin can produce the same hypersensitivity reaction as ampicillin in the setting of acute infectious mononucleosis. The clinical decision to use antibiotics in acute pharyngitis is complicated by the identical presentation of both viral and bacterial illnesses. If empiric therapy is elected, the incidence of hypersensitivity reaction is less common with penicillin or tetracycline compared to ampicillin or its analog, amoxicillin.