Prevalence and spot urine risk factors for renal stones in children taking topiramate

Introduction: Topiramate (TPM), an anti-epileptic drug with > 4 million users, increases renal stones in adults. We screened outpatient TPM-treated children without history of stones to estimate the prevalence of renal stones and to characterize urine stone-risk profiles. Methods: Children taking TPM >= 1 month underwent an interview, renal ultrasound, and spot urine testing in this prospective study. Normal spot urine values were defined as: calcium/creatinine ratio <= 0.20 mg/mg (> 12 months) or <= 0.60 mg/mg (<= 12 months), citrate/creatinine ratio > 0.50 mg/mg, and pH <= 6.7. Results: Of 41 patients with average age of 9.2 years (range 0.5-18.7), mean TPM dose of 8.0 mg/kg/day (range 1.4-23.6), and mean treatment duration of 27 months (range 1-112), two (4.9%) had renal stones. The majority of children taking TPM had lithogenic abnormalities on spot urine testing, including 21 (51%) with hypercalciuria, 38 (93%) with hypocitraturia, and 28 (68%) with pH >= 6.7. Hypercalciuria and hypocitraturia were independent of TPM dose and duration; urine pH increased with dose. 24-h urine parameters improved in 1 stone-former once TPM was weaned. Conclusions: Asymptomatic stones were found in 2/41 (4.8%) children taking TPM. Risk factors for stones were present in the spot urine of most children, including hypocitraturia (93%) and hypercalciuria (51%), independent of TPM dose and duration. High urine pH, found in 68%, correlated with TPM dose. Pediatric specialists should be aware of increased risks for stones, hypercalciuria, hypocitraturia, and alkaline urine in children taking TPM. Published by Elsevier Ltd on behalf of Journal of Pediatric Urology Company.