Abstract
Mesalazine-induced pericarditis is rare, and most cases occur at the time of treatment initiation. A 30-year-old man with ulcerative colitis who had experienced remission for 2 years with mesalazine 2,000 mg/day subsequently experienced relapse. Therefore, the mesalazine dose was increased to 4,000 mg. Thereafter, hematochezia improved, but anterior chest pain developed. Chest radiography revealed marked cardiac dilation (cardiothoracic ratio, 63%) and echocardiography revealed pericardial effusion. Adverse events associated with mesalazine should be carefully monitored, not only at the time of treatment initiation but also after dose escalation.