This Amendment has been issued following a Special Protocol Assessment performed by the USA FDA on SP0969 (NCT01921205). Where applicable, the recommendations made by the FDA have been incorporated into the current protocol. Major changes: •Dosing was changed to match SP0969 (based on subject weight) •Inclusion criteria for concomitant antiepileptic drugs (AEDs) and vagus nerve stimulation (VNS) were modified to match SP0969 •Subjects with primary generalized tonic-clonic seizures with a diagnosis of idiopathic generalized epilepsy were excluded. The effect of lacosamide (LCM) in this population is planned to be investigated in a confirmatory study •Exclusion criteria for felbamate and vigabatrin were modified •The Behavior Rating Inventory of Executive Function was added as an additional safety assessment •The Pediatric Quality of Life Inventory was added as an additional efficacy assessment •Health care resource use was added as an efficacy variable •The requirement to measure height was restricted to visits with a complete physical examination •Withdrawal criteria based on the use of rescue medication was added •An additional assessment at end of titration was added for the Achenbach Child Behavior Checklist. •Orthostatic blood pressure and pulse assessments were added •Concomitant, prohibited and rescue medications were modified to match SP0969 •The terminology “syrup” was replaced with oral solution •Assessment time points for scales and questionnaires were modified •Additional assessments for VNS assessments and urinalysis were added •The number of sites was increased to 40 •Additional text was added clarifying which version of the Columbia Suicide Severity Rating Scale (C-SSRS) should be used at study entry and for subjects turning 6 years of age. •Administrative changes •Typographical changes

The present amendment has been issued following additional feedback from the USA FDA on both SP0969 and SP0966. Where applicable, the recommendations made by the FDA have been incorporated into the current protocol. In addition, updates were made for consistency with other lacosamide (LCM) protocols. The following major changes were made: •The titration and taper schedules were changed to include different weight categories, a 600 mg/day LCM dose, and an extended (slower) titration schedule. •The schedule of assessments was modified to include the changes to the titration schedule, additional visits, and changes to the assessments at each visit. •The schematic diagrams were updated to reflect the additional changes to the titration and taper schedules. •Inclusion criteria were modified to allow inclusion of subjects with West syndrome. •Measurements of head circumference were included. •The language regarding unscheduled visits was updated to make it clear that investigators can perform additional procedures based on their judgment and medical need. •The age allowed for initial enrollment was reduced from 4 to 2 years. •The duration of the safety follow-up was made consistent with other LCM studies (SP0969). •The definition of end of study for the subjects has been clarified to account for subjects who enter and do not enter the open-label study. •Additional language was added describing the procedures if the study is completed and the taper is not required at the end of the study. •The language regarding study medication storage has been updated according to the clinical label. •The language regarding some of the scales used in this study has been updated for clarification. •The number of sites and countries in the study were increased. •Administrative changes •Typographical changes

The following key changes were made throughout the protocol: •Subjects with primary generalized tonic-clonic seizures (PGTCS) with a diagnosis of idiopathic generalized epilepsy (IGE) are not excluded from the study population. •Subjects >=1 month to <2 years of age can now be enrolled into SP0966. •Subjects with second- or third-degree heart block are excluded from SP0966, without the requirement of being at rest. •The atrioventricular (AV) block withdrawal criterion was modified to second or third degree AV block, without the requirement of being awake. •Head circumference is to be measured only in subjects <4 years of age. •Administrative changes: the name and details of the Clinical Project Manager and the Serious Adverse Event (SAE) Reporting Email address were updated.

The following key changes were made throughout the protocol: •Subjects with primary generalized tonic-clonic seizures with a diagnosis of idiopathic generalized epilepsy were excluded from the study population. •Exclusion criterion for creatinine clearance rate has changed from <50 milliLiters/minute (mL/min) to <30 mL/min. •Exclusion criterion number 20 has been reworded to clarify that the excluded sodium channelopathies are cardiac. •Administrative changes: the name of the Study Physician and the name of the contract research organization (CRO) have been updated, and the Sponsor Declaration has been updated for electronic signature. •Russia has been removed as a participating country.