Evaluation Phenobarbital as Adjunctive Therapy in Participants With Partial Onset Seizures

Primary: -to evaluate the efficacy of once daily (OD) administration of 60 mg and 100 mg phenobarbital, in reducing seizure frequency in participants with partial onset seizures (Type I seizures; complex or simple with motor symptoms only) not fully controlled despite treatment with 1 to 3 concomitant anti-epileptic drugs (AEDs) or AEDs with Vagus Nerve Stimulator (VNS) Secondary: * to confirm dose response relationship of 60 and 100 mg phenobarbital doses, * to assess the effects of phenobarbital on Type I seizures, * to assess the safety of phenobarbital * to assess the tolerability of phenobarbital