A 15-year-old male suddenly screamed, fell to the ground, exhibited upward eye deviation, convulsions of the limbs, and cyanosis lasting about 5 minutes before gradually regaining consciousness without discomfort. A similar episode occurred 5 years ago. EEG one week ago was normal. Neurological examination showed no abnormalities. During follow-up one week later, he reported two more episodes yesterday afternoon and this morning with identical symptoms. The first-line treatment drug is: