To evaluate the efficacy , tolerability , and safety of once-daily 1200 mg and 2400 mg SPN-804 ( Oxtellar XR , Supernus Pharmaceuticals ) , an extended-release tablet formulation of oxcarbazepine ( OXC ) , added to 1-3 concomitant antiepileptic drugs ( AEDs ) in adults with refractory partial-onset seizures , with or without secondary generalization .