Mesalazine-induced nephrolitiasis and crystalluria.

Mesalazine (5-aminosalicylic acid) is an anti-inflammatory drug used for autoimmune diseases. Premature release mesalazine in the small intestine or proximal colon can increase systemic absorption. A 13-year-old with ulcerative colitis treated with Pentasa® at 2 g mesalazine/day developed stones when this dose was doubled. Mesalazine has low water solubility; higher doses raise urinary supersaturation, promoting epitaxial growth of mesalazine crystals that form a stone. In children, lower body weight and reduced urine volume increase this risk. Dose adjustment and adequate hydration are essential, as low urine output raises mesalazine concentration and favors crystallization. Increased fluid intake is strongly recommended.