The purpose of this study was to determine the incidence and potential predictors of weight gain in older children and teens treated with valproate (VPA) for epilepsy.

Sixty-five subjects aged 8 to 17 years of age, who began VPA treatment between January 1, 2001, and December 31, 2004, and who had documented weight and height measurements at medication initiation and at least one follow-up visit were retrospectively identified. Exclusion criteria were follow-up <6 months, discontinuation of VPA within 6 months, and concurrent therapy with medication known to affect weight (such as topiramate, carbamazepin). Body mass index (BMI) was calculated at initiation and either discontinuation of VPA or last follow-up and stratified into four categories: group 1, underweight <5%; group 2, appropriate 5-85%; group 3, potentially overweight 85-95%; group 4, overweight >95%.

Twenty-eight subjects (77.8%) remained within their same category and eight (22.2%) moved up at least one category. Weight gain (increase in BMI difference) was observed in 72.2% of the 36 subjects treated with VPA. Three factors, neurocognitive status ( P =0.017), seizure type ( P =0.001) and duration of VPA treatment ( P =0.035) were identified to be significant predictors of BMI difference.

VPA induces weight gain in children and teens with epilepsy. These factors which are normal neurocognitive status, primary generalized type and duration of VPA treatment over the 12 months were predictors for an increase of weight gain. Therefore potential weight gain should be discussed with patients before the initiation of therapy and BMI should be monitored closely.