A Trial to Evaluate the Efficacy and Safety of Adjunctive Therapy With Lacosamide in Adults With Partial-Onset Seizures

Inclusion Criteria: * Subject has had an Electroencephalogram (EEG) and a brain Computerized Tomography (CT) scan or Magnetic Resonance Imaging (MRI) exam consistent with a Diagnosis of Epilepsy with Partial-Onset Seizures according to the International Classification of Epileptic Seizures (1981) * Subject must have been observed to have Partial-Onset Seizures for at least the previous 2 years despite prior therapy with at least 2 Anti-Epileptic Drugs (AEDs)(concurrently or sequentially) and must have been observed to have on average at least 4 Partial-Onset Seizures per 28 days with a seizure-free phase no longer than 21 days in the 8-Week Period prior to entry into the Baseline Period. In the case of Simple Partial Seizures, only those with motor signs will be counted towards meeting the inclusion criterion * Subjects must be on a stable dose regimen of at least 1, but no more than 3 AEDs (concurrent stable Vagus Nerve Stimulation (VNS) is not counted as an AED). The VNS must have been in place for at least 6 months prior to study entry. The dosage of concomitant AED therapy and the settings of the VNS must be kept constant for a period of at least 4 weeks prior to entry into the Baseline Period * Minimum Body Weight of 40 kg Exclusion Criteria: * Subject has a lifetime history of suicide attempt (including an active attempt, interrupted attempt, or aborted attempt) or has a suicidal ideation in the past 6 months as indicated by a positive response ("Yes") to either Question 4 or Question 5 of the Columbia-Suicide Severity Rating Scale (C-SSRS) at Screening * Subject has a current or previous diagnosis of Pseudo-Seizures, Conversion Disorders, or other non-epileptical events that could be confused with Seizures * Subject has Seizures that are uncountable due to Clustering (ie, an episode lasting less than 30 minutes in which several Seizures occur with such frequency that the initiation and completion of each individual Seizure cannot be distinguished) during the 8-Week Period prior to Visit 1 * Subject has a history of Primary Generalized Seizures * Subject with a history of Status Epilepticus within the 12-Months Period prior to Visit 1 * Subject who underwent surgery for Epilepsy within the 2 Years Period prior to Visit 1 * Subjects with cardiac, renal, hepatic, endocrinological dysfunction or psychiatric illness that may impair reliable participation in the study or necessitate the use of medication not allowed by the protocol