A17-year-old girl presents 2 days following a generalized seizure, her second in 6 months. both seizures occurred between 3 am and 6 am while she was sleeping, in the week before her menses. her medical history is unremarkable and she takes no medications. results of physical and neurologic examinations are normal, and a pregnancy test done in the emergency department is negative. eeg shows activity consistent with a generalized seizure disorder. what medication is best at this time?