Famotidine-Induced Rash and Eosinophilia: A Case Report

We report the case of a 77-year-old man who was admitted with a urinary tract infection and concurrent influenza A, who subsequently developed an unusual hypersensitivity reaction to famotidine. He initially received intravenous gentamicin followed by oral amoxicillin-clavulanic acid for the urinary tract infection. Oseltamivir and carbocisteine were prescribed for the flu. During admission, his proton pump inhibitor (PPI) was switched to famotidine due to hyponatremia. Four days later, he developed an itchy, erythematous maculopapular rash on his arms and legs. Initially localized to both extensor and flexural areas, the rash progressively spread to involve his torso over the next few days. A significant rise in eosinophils raised suspicion of a drug-induced reaction. Considering the timing of the rash and the patient's lack of prior adverse reactions to penicillin, famotidine was identified as the most probable causative agent for the rash. The rash improved following discontinuation of famotidine, supporting the diagnosis of famotidine-induced hypersensitivity reaction.