A 19-year-old man presents with fever, sore throat, cervical lymphadenopathy, and splenomegaly. He was started on ampicillin one week ago for presumed bacterial pharyngitis and has now developed a generalised maculopapular eruption. The single most likely explanation for the rash is:

• A True IgE-mediated allergy to ampicillin requiring lifelong penicillin avoidance
• B Ampicillin-induced toxic epidermal necrolysis
• C Serum sickness reaction due to ampicillin
• D Non-allergic ampicillin rash occurring in the setting of Epstein-Barr virus infection ✓

Explanation

A maculopapular eruption after ampicillin or amoxicillin in a patient with infectious mononucleosis is a classic non-allergic cutaneous reaction, seen in a large proportion of EBV-infected patients given these drugs, and it does not indicate true penicillin allergy. Rechallenge later without EBV infection is usually tolerated. Serum sickness features fever, arthralgia, urticaria and proteinuria, which are absent here, and there is no mucosal detachment to suggest SJS/TEN.

Reference: Fitzpatrick's Dermatology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.