Rapid Onset of Mesalazine-Induced Eosinophilic Pneumonia Manifesting 7 Days After Initiation: A Case Report.

Mesalazine is a recognised cause of drug-induced eosinophilic pneumonia. The condition usually occurs after 2-6 months of therapy, and onset within the first week is rare. A 29-year-old woman with bronchial asthma and newly diagnosed ulcerative colitis was initiated on oral mesalazine. On Day 7, she developed a persistent cough. Three weeks later, imaging revealed a right upper-lobe pulmonary infiltrate, promoting referral for evaluation. Bronchoalveolar lavage and transbronchial cryobiopsy demonstrated marked eosinophilic infiltration, confirming eosinophilic pneumonia. Discontinuation of mesalazine led to rapid clinical and radiographic improvement. Clinical course and exclusion of alternative aetiologies identified mesalazine as the causative drug. This case demonstrates that mesalazine can induce eosinophilic pneumonia within 7 days of initiation.