Abstract
Trimethoprim-Sulfamethoxazole is a commonly used antibiotic for treatment of urinary tract infections, but also used to treat less common conditions such as pulmonary nocardiosis. N4-acetyl-sulfamethoxazole is the main active metabolite of Sulfamethoxazole. Pure stones of this compound are very rare with only a few cases documented in the literature. Here we present a case of a patient treated with long term trimethoprim-sulfamethoxazole therapy for pulmonary nocardiosis who developed pure N4-acetyl-sulfamethoxazole nephrolithiasis resulting in upper tract obstruction. This report provides an additional data point for this unique calculus etiology.