Abstracts

RATIONALE: This is a prospective study to assess the risk of developing renal stones or nephrocalcinosis in paediatric patients put on topiramate (TPM) for the treatment of epilepsy.
METHODS: Patients less than 16 years of age, whom TPM was to be added on in the treatment of poorly controlled epilepsy were enrolled. The parents were informed of the risk of renal stones of 1.5% in adults using TPM [Epilepsia 1996; 37(Suppl. 4): S74]. Renal ultrasound recordings of the longitudinal and transverse sections of both kidneys were obtained just before starting TPM, at 6 months, and at 12 months for patients who were still on it, using the Diasonics Ultrasound Multisync M500 or GE Ultrasound System RT2800. Frank renal stones were first looked for in the kidneys and bladder. In the absence of stones, the renal sonogram was further classified based on the nephrocalcinosis grading scale. Grade 0 is used when there are no abnormalities in the medullary pyramids, grade I when there is mild increase in echogenicity around the border of the medullary pyramids, grade II being mild diffuse increase in echogenicity of the entire medullary pyramids, and grade III being homogenous increase in echogenicity of the entire medullary pyramids.
RESULTS: Twenty-two patients (11 males and 11 females) with the mean age of 7 years 9 months were included in the study. Ten patients were on one anti-epileptic drug (AED), 8 were on two AEDs, and 4 were on three AEDS prior to starting TPM. These various AEDs included carbamazepine, valproic acid, phenytoin, phenobarbitone, lamotrginie, vigabatrin, nitrazepam, clobazam and clonazepam. None were on acetazolamide, zonisamide or ketogenic diet. The average dose of TPM 6 months after starting treatment was 8.96mg/kg/day, with the range from 1.58 mg/kg/day to 22.73mg/kg/day. Twenty patients were on doses above 6 mg/kg/day, based on the minimum effective dose suggested for TPM in children. [Can J Neurol Sci 1998; 25: S8-S12]. On follow-up six months later, all 22 patients had normal renal sonograms, with no evidence of frank renal stones or nephrocalcinosis. Twelve patients continued to be treated with TPM. At 12 months, their average dose of TPM was 7.92mg/kg/day with the range being from 0.92 mg/kg/day to 11.50mg/kg/day. Nine of the 12 patients were on TPM dose above 6mg/kg/day. Their renal sonograms at 12 months were all normal.
CONCLUSIONS: This study suggests low risk of developing renal stones or nephrocalcinosis in paediatric patients using TPM after 6 months to a year.
[Supported by: Department of Pediatrics, National University Hospital, Singapore.]