This study is to evaluate the efficacy of YKP3089 in reducing seizure frequency when compared to baseline in subjects with partial onset seizures not fully controlled despite their treatment with 1 to 3 concomitant anti-epileptic drugs.

Also to evaluate the safety and tolerability of YKP3089.

Inclusion Criteria:

• Diagnosis of treatment resistant partial epilepsy;

• History of epilepsy for at least 2 years;

• Have at least 3 simple partial with motor component, complex partial or secondarily generalized seizures per month with no consecutive 21 day seizure free period.

• Currently treated on a stable dose of :

  • 1 - 3 AED's for at least 12 weeks prior to randomization.
  • VNS will not be counted as AED; however the parameters must remain stable for at least 4 weeks prior to baseline.
  • Benzodiazepines taken at least once per week for epilepsy, or for anxiety or sleep disorder, will be counted as 1 AED. Therefore only a maximum of two additional approved AEDs will be allowed.

Exclusion Criteria:

1. A history of alcoholism, drug abuse, or drug addiction within the past 2 years.
2. Subject has had status epilepticus within past 1 year.
3. Subject has had greater than 2 allergic reactions to an AED or one serious hypersensitivity reaction to an AED.
4. Subjects taking felbamate with less than 18 months continuous exposure.
5. Subjects receiving phenytoin, phenobarbitone or metabolites of these drugs.
6. No active suicidal plan/intent or active suicidal thoughts in the past 6 months.
7. History of suicide attempt in the last 2 years; not more than 1 lifetime suicide attempt.
8. Subject meets criteria for current major depressive episode (within 6 months).
9. Use of intermittent rescue benzodiazepines more than once/month (1-2 doses in a 24-hour period is considered one rescue) in the one month period prior to Visit 1.