Dear Editor: Mesalazine (5-aminosalicylic acid) is a medication widely used in the management of inflammatory bowel disease (IBD). The precise mechanism of mesalazine action remains poorly understood. However, it has been proposed that the drug acts locally on the colonic mucosa reducing inflammation through a variety of anti-inflammatory processes. These processes include the inhibition of proinflammatory cytokines (interleukin-1, interleukin-2, and interleukin-8 and tumor necrosis factor-α), the induction of the proliferator-activated receptor-γ gene expression, or mesalazine acting as a potent antioxidant and free radical scavenger. The use of mesalazine in the treatment of IBD has been limited by the side effects, most of them secondary to the sulfapyridine component. On the other hand, the use of mesalazine is usually well tolerated by patients, due to its favorable safety profile. Due to a limited number of cases of mesalazine-induced pulmonary disease, it has been difficult for clinicians to diagnose these diseases early. We report a case of lung hypersensitivity caused by mesalazine therapy in a patient with ulcerative colitis (UC). A short review of the literature on mesalazine-induced lung disease in IBD patients is also presented.Our patient is a 39-year-old non-smoking woman with 2 months history of UC treated with mesalazine (3.6 g/day) since the initial UC diagnosis. She was admitted to the hospital with 2 weeks history of cough, fever, progressive dyspnea, and night sweats. On admission, she was febrile (38.5°C). Her blood pressure was 120/82 mmHg, her heart rate was 90/min, and her SaO 2 was 93 % on ambient air. The remaining physical examination revealed crackles at the lower pulmonary fields. Laboratory studies showed a leukocyte count of 9970/μL, with 68.3 % neutrophils and 8.1 % eosinophils (normal range 1-6 %). The erythrocyte sedimentation rate was 114 mm/h and C-reactive protein 4.5 mg/dL (normal range <0.5 mg/dL). The patient was hypoxemic with arterial blood gases analyses revealing a pH of 7.44, an oxygen saturation of 93 %, a partial pressure of oxygen of 61 mmHg, and a partial pressure of carbon dioxide of 34 mmHg, while breathing on ambient air. Chest X-ray examination showed bilateral pulmonary infiltrates. Levofloxacin and ceftriaxone were empirically started to treat presumed community-acquired pneumonia, and therapy with mesalazine was continued. Nevertheless, the patient continued to have cough, fever, and dyspnea. A computed tomography (CT) scan revealed the presence of peripheral alveolar infiltrates. Urine examination for Streptococcus pneumoniae and Legionella antigen was negative. A two-

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