Objectives: To compare the 12-month retention rate, effectiveness and tolerability of perampanel (PER) as a first or late add-on treatment in adult patients with focal-onset seizures (FOS), including focal to bilateral tonic-clonic seizures (FBTCS). Methods: This retrospective, observational, multicenter study was carried out in patients with FOS that received PER as a late add-on (n = 60), after failure of > 3...