N4-acetyl-sulfamethoxazole stone in a patient on chronic trimethoprim/sulfamethoxazole therapy: a case report and literature review.

Though early antibiotic sulfonamides had poor urine solubility and resulted in urine crystalluria and urolithiasis, sulfamethoxazole urolithiasis is a rare phenomenon. In our case report, we describe a patient with N4-acetyl-sulfamethoxazole (metabolite of sulfamethoxazole) urolithiasis that developed after prolonged exposure to trimethoprim/sulfamethoxazole (TMP-SMX). Prior to stone formation, our patient had a total colectomy and end ileostomy created after an episode of toxic megacolon secondary Clostridium difficile. He also had benign prostatic hypertrophy and chronic urinary retention. These specific metabolic conditions, including dehydration leading to higher urinary concentration, urinary stasis, and low urinary pH may have predisposed our patient to this rare condition. Our patient's stones were then imaged under light microscopy and scanning electron microscopy (SEM). It was found to be comprised of rectangular shaped crystals. To our knowledge, this is the first time these stone crystals have been imaged with SEM.