Acute Localized Exanthematous Pustulosis Due to Metronidazole

A 78-year-old male patient developed acute localized exanthematous pustulosis (ALEP) after taking oral metronidazole for rosacea treatment. The onset of multiple non-follicular pustules on his face occurred 2 days post-initiation of the medication. The patient's physical examination showed pustules on an erythematous, edematous background without mucous or joint involvement. Laboratory tests indicated a slight increase in white blood cells and inflammatory markers, but liver and renal functions were normal, and cultures for bacteria, fungi, and HSV were negative. A skin biopsy confirmed ALEP, and a patch test for metronidazole was positive. The patient's treatment with metronidazole was stopped, and he was treated with systemic methylprednisolone, leading to rapid resolution of the pustules within 5 days and reduction of erythema after 1 week. This case is notable as it appears to be the first reported instance of ALEP caused by metronidazole, a drug rarely associated with allergic reactions, with less than 2% of patients with confirmed drug reactions being allergic to it.