My brother

Okay so. My brother first had a seizure back in 06’ (12 yrs old) and was seizure free for years up until 2014 (21 yrs old). After then he was seizure free for 4 years and started having seizures more frequently from 2018 to now. Maybe 2-3 a year. He’s been on keppra for the last 4 or so years. Anyone here have any idea why it seems to have gotten worse? We just don’t understand why.