Long-Term Safety Study of Retigabine Immediate Release (IR) as Adjunctive Therapy in the Treatment of Adults With Partial-Onset Seizures (POS)

RTG113413 is an open-label, multicentre extension study of RGB113905. This study will enroll adult subjects with partial-onset seizures (POS) who successfully completed 20 weeks of adjunctive treatment with retigabine IR (4-weeks Titration Phase and 16-weeks Flexible Dose Evaluation Phase) in the parent study, RGB113905 and who were thought to have benefitted from the treatment. The Screening Visit (Visit 1) will be performed on the same day as the final visit of the parent study (Visit 7/Week 20). Subjects entering the extension study will initially receive the same dose of retigabine IR and concurrent antiepileptic drug (AED) as they were receiving on the final visit of the parent study. After the first week of the extension study, the subject's retigabine dose can be adjusted based on efficacy and tolerability. The overall daily dose of retigabine IR must be maintained between 300 mg/day (minimum) and 1200 mg/day (maximum). In addition, the dose and the number of concurrent AEDs can be adjusted to meet the individual needs of the subject. Retigabine IR monotherapy is not permitted. If concurrent AED therapy is removed, the subject must be withdrawn from the study. Subjects in this study will be eligible to receive retigabine IR treatment until one of the following criteria have been met: 1) regulatory approval and commercial availability of retigabine IR or 2) retigabine IR is not approved by the regulatory authorities or 3) the study is terminated by the sponsor for reasons including, but not limited to, safety issues or 4) subject is withdrawn or withdraws consent or 5) subject has received retigabine IR treatment for a total of 3 years and options i-iv have not been met. After the Screening Visit, subjects will be required to attend 4 further clinic visits at Weeks 13, 26, 39, and 52 in the first year of the study and a total of 3 clinic visits at approximately 4-monthly intervals during each of the second and third year of study. Upon completion or early withdrawal, subjects will begin a 3-week taper period and then return for a follow-up visit.