Seizure Disorders USMLE Step 1 Practice Question

A 7-year-old boy is brought to clinic by his mother who reports that he has been having multiple episodes daily where he suddenly stops what he is doing, stares blankly ahead, and flutters his eyelids for several seconds before returning to normal activity. She estimates each episode lasts 3-5 seconds and occurs 15-20 times per day, often during homework or meals. The patient was diagnosed with childhood absence epilepsy 6 months ago and was started on ethosuximide. Physical examination is unremarkable with no focal neurologic deficits. An EEG recorded during one of the episodes shows the characteristic 3 Hz spike-and-wave pattern. A serum ethosuximide level drawn 2 hours after the morning dose is 32 mcmol/L (therapeutic range: 40-100 mcmol/L). The patient reports good medication adherence and has experienced no adverse effects. Which of the following is the most appropriate next step in management?