Primary:

- to evaluate the efficacy of phenobarbital in reducing seizure frequency.

Secondary:

• to confirm dose response relationship,
• to assess the effects on Type I seizures,
• to assess the safety of phenobarbital
• to assess the drug tolerability.

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

Inclusion Criteria:

• participants from 17 to 70 years old;
• history of Type I partial onset seizures (complex or simple with motor symptoms only);
• participants must have had electroencephalogram (EEG), magnetic resonance imaging (MRI) or computed tomography (CT) with results consistent with diagnosis of partial-onset seizures;
• participants having at least eight Type I partial onset seizures during 8-week baseline period;
• participants being uncontrolled while treated by 1 to 3 permitted concomitant anti-epileptic drug (AED) and/or Vagus Nerve Stimulation (VNS);
• participant has been on a stable dose of their current anti-epileptic treatment regime

Exclusion Criteria:

• currently taking phenobarbital or primidone;
• currently taking felbamate or vigabatrin;
• history of prior allergic reaction to phenobarbital;
• history of psychogenic seizures;
• history or presence of status epilepticus;
• history or presence of seizures occurring only in clusters;
• participant taking any drug with possible Central Nervous System (CNS) effects except if stable from 1 month prior Visit 1;
• history of cerebrovascular accident (CVA) or transient ischemic attack (TIA);
• presence of any sign suggesting rapidly progressing brain disorder or brain tumor;
• presence of unstable arteriovenous malformations, meningiomas or other benign tumors;
• history of porphyria;
• presence of clinically significant findings on physical exam, vital signs, electrocardiogram (ECG) or safety lab assessments, including renal or hepatic insufficiency;
• history of alcohol or drug abuse within the year prior to screening;
• participant who is known to be non-compliant;
• participant who is male or female who refuses to use an acceptable form of contraception;
• female who is pregnant or lactating or intends to become pregnant;
• participant who has taken part in any investigational device or product within 2 months prior to the screening visit