Long-term, Open-label Safety Extension Study of Retigabine/Ezogabine in Pediatric Subjects (>= 12 Years Old) With POS or LGS

The purpose of this study is to evaluate the long-term safety and tolerability of retigabine/ezogabine as an adjunctive treatment in subjects with either partial onset seizures (12 to \< 18 years old) or Lennox-Gastaut Syndrome (12 to \<30 years old) who have participated in a previous ("parent") study.

Epilepsy is among the most common serious neurologic disorders in childhood. Medicines with novel actions of mechanisms of action are needed to try to address the unmet clinical need for seizure control in patients with treatment-resistant epilepsy. The purpose of this study is to evaluate the long-term safety and tolerability of retigabine/ezogabine as an adjunctive treatment in subjects with either partial onset seizures (12 to \< 18 years old) or Lennox-Gastaut Syndrome (12 to \<30 years old) who have participated in a previous ("parent") study.

Eligibility Criteria:
Inclusion Criteria:

* Has participated in either a Phase II or Phase III retigabine/ezogabine clinical trial evaluating partial onset seizures or seizures comprising Lennox-Gastaut syndrome and met the requirements defined in the parent study to transition into the open-label extension study
* Investigator and caregiver consider it beneficial for the patient to continue treatment with retigabine/ezogabine
* Female subjects of child-bearing potential (after menarche) must either not be sexually active or must be practicing an acceptable method of contraception (documented in the medical chart) from two weeks prior to administration of study medication and for 28 days after completion or premature discontinuation from the study
* Subject is living with his/her custodial parent(s) or legal guardian(s) and has contact with them on a daily basis
* Written informed consent is obtained from the subjects parent/guardian and accompanying assent from subject. The subject, and/or his/her custodial parents(s) or legal guardian(s) have the ability to comprehend the key components of the informed consent form

Exclusion Criteria:

* Has insufficient ability to articulate the presence or absence of urinary tract symptoms
* Has experienced an adverse event, clinically significant laboratory abnormality or was discontinued from the parent study due to a reason that in the investigator's judgment would preclude enrollment to the study
* Has a urine sample with: Urine specific gravity \>1.035, Urine pH \<4.6 or \>8.0, ≥2+ proteinuria, Casts or crystals (any type), \>5 RBC/HPF, unrelated to menses
* Has a blood sample with: BUN \>21 mg/dl for 12 year old, or \>25 mg/dl for \>12 year old, Creatinine \>1.03 mg/dl (F), or \>1.3 mg/dl (M), Uric acid \>7.5 mg/dl (F), or \>8.5 mg/dl (M), Chloride \>108 mEq/L, parameters for calcium, inorganic phosphorous or CO2 that are clinically significant as judged by the investigator
* Has presence of clinically significant hepatic laboratory values: aspartate aminotransferase (AST) and alanine aminotransferase (ALT) \>2x upper limit of normal (ULN); alkaline phosphatase and bilirubin ≥1.5xULN (isolated bilirubin \>1.5ULN is acceptable if bilirubin is fractionated and direct bilirubin \<35%
* Has presence of clinically significant cardiac arrhythmias
* Has any abnormality on 12-lead ECG which is clinically significant in the opinion of the investigator, or has a corrected QT interval (using either Bazett's or Fridericia's) \>500msec ( \>530 msec for subjects with Bundle Branch Block), uncorrected QT interval \>600msec, or change from baseline QTc \>60msec
* Has a history of one or more renal calculi
* Has disturbances of micturition or known urinary obstructions, including renal calculi
* Has a documented anatomical stricture or other anatomical abnormality of the urinary tract system that has the potential to interfere with urinary flow
* Has experienced clinically significant urinary retention and/or required urinary catheterization in the preceding 6 months
* Has experienced 2 or more objectively documented urinary tract infections in the preceding 12 months
* Has a history of inadequate fluid intake and clinically significant dehydration in the preceding 6 months
* Within the preceding month, has taken anti-cholinergic medication on an ongoing basis
* Has active suicidal plan/intent or has had active suicidal thoughts in the past 6 months or has history of suicide attempt in the last 2 years or more than one lifetime suicide attempt
* Is planning surgery or implantation of a vagus nerve stimulator to control seizures during the study
* Is currently or has been abusing substance(s) or any medications in the 12 months prior to study entry
* Has taken an investigational drug (exception retigabine/ezogabine), or used an investigational device, within the previous 30 days prior, or plans to take an investigational drug anytime during the study
* Females who are lactating or are pregnant
* Unwillingness or inability to follow the procedures outlined in the protocol
* The subject is felt, by the investigator, to be unsuitable for inclusion in the study
* Children in care