Objectives: 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.
Methods: 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.
Results: 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).
Conclusions: 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.
Copyright © 2011 Elsevier Inc. All rights reserved.