To determine the effect of topiramate (TPM) on 24-hour urinary parameters in stone formers. TPM is frequently prescribed for epilepsy, migraine headaches, and eating disorders.

Twelve stone-forming patients who were prescribed TPM between 2003 and 2008 were identified from our stone clinic. Of these, 9 patients (M:F, 4:5; 47 ± 7.1 y SEM) underwent a full metabolic workup (UroRisk Diagnostic Profile, Mission Pharmacal Reference Laboratory, San Antonio, TX) and were included for review. Parameters examined include duration and dose of the drug, 24-hour urine calcium, oxalate, citrate, volume, and pH. If available, urine parameters before taking TPM and after either stopping it or receiving potassium citrate therapy were recorded.

Mean duration taking TPM was 17 ± 5.2 months (range, 3-43) months and median dose was 100 mg (range, 25-300) daily. Mean urinary citrate excretion was 136 ± 29 mg/d (range, 30-280) in all patients taking the drug. Three patients were either taken off the drug or placed on potassium citrate, resulting in a mean increase in urinary citrate of 374 mg/d (65%). TPM dosage correlated inversely with urinary citrate excretion (Pearson correlation coefficient = −0.73).

TPM therapy is associated with a profound, dose-dependent decrease in urinary citrate, leading to increased lithogenic risk. This hypocitraturia persists even after long periods of taking the drug. Urologists should be aware of the stone-forming risk of this medication. Strategies to maintain therapeutic urinary citrate concentrations in patients on TPM are needed.