A Study to Assess the Safety and Efficacy of Lacosamide Versus Placebo (a Pill Without Active Medication) in Patients With Idiopathic Generalised Epilepsy Who Are Already Taking Anti-epileptic Medications

Inclusion Criteria: * Subject with a confirmed diagnosis at least 24 weeks prior to Visit 1 and a disease onset prior to 30 years of age, consistent with idiopathic generalized epilepsy (IGE) experiencing primary generalized tonic-clonic (PGTC) seizures (Type IIE) that are classifiable according to the International League Against Epilepsy (ILAE) Classification of Epileptic Seizures (ILAE, 1981) * Subject has \>=3 PGTC seizures during the 16-week Combined Baseline (12-week Historical Baseline plus 4-week Prospective Baseline) * If a brain magnetic resonance imaging (MRI)/computed tomography (CT) scan has been performed, there must be no evidence of any progressive abnormality or any lesion likely to be associated with partial-onset seizures * Subject has been maintained on a stable dose regimen of 1 to 2 non-benzodiazepine marketed antiepileptic drugs (AEDs) with no benzodiazepine AEDs OR 1 benzodiazepine marketed AED with 1 to 2 non benzodiazepine marketed AEDs for at least 28 days prior to Visit 1 with or without additional concurrent stable vagus nerve stimulation (VNS) * Subjects are required to have had an electroencephalogram (EEG) report consistent with idiopathic generalized epilepsy (eg, generalized 3Hz epileptiform discharges and a normal EEG background) confirmed by a Central Reviewer Exclusion Criteria: * Subject is receiving any investigational drugs or using any experimental devices in addition to Lacosamide (LCM) * Subject meets the withdrawal criteria for S…