Study of Retigabine Immediate Release as Adjunctive Therapy to Specified Monotherapy Antiepileptic Treatments in Adults With Partial-Onset Seizures

The purpose of this Phase III study is to evaluate the efficacy, safety and tolerability and health outcomes of retigabine Immediate Release (IR) as adjunctive therapy to each of the following monotherapy Antiepileptic Drug (AED) treatments: carbamazepine/oxcarbazepine, lamotrigine, levetiracetam, or valproic acid in adult subjects with partial-onset seizures (POS) using a flexible dosing regimen.

This is an open-label, multi-centre, flexible dose study of retigabine immediate release (IR). The study will enroll male and female outpatients (≥ 18 years of age) with partial-onset seizures (POS) who are inadequately controlled on their current monotherapy Antiepileptic Drug (AED). Following a Screening Period of up to 2 weeks, subjects will enter an 8-week Baseline Phase to determine baseline seizure frequency. At the end of the Baseline Phase, subjects who meet or exceed the minimum seizure frequency of 4 partial seizures per 56 days, will enter the Treatment Period (4 weeks Titration, 16 weeks Flexible Dose Evaluation Phase). All subjects will receive retigabine IR starting at 150 mg/day and will be titrated to 600 mg/day by Week 4. From Week 5 onwards, subjects' doses will be maintained between 300 to 1200 mg/day using a flexible dosing regimen to optimise response and tolerability. The maximum duration of the study is approximately 33 weeks (inclusive of a 3 week Taper/Follow-up Phase).

Eligibility Criteria:
Inclusion Criteria:

* Is 18 years of age (men or women)
* Has a confident diagnosis of epilepsy with partial-onset seizures i.e., simple or complex partial seizures with or without secondary generalization (International League Against Epilepsy (ILAE) classification; 1981) for more than 24 weeks prior to the start of Baseline phase.
* Has experienced at least 4 partial-onset seizures (i.e., simple or complex partial seizures with or without secondary generalization) during an 8-week (i.e., 56 days) prospective Baseline Phase with at least one partial seizure occurring during each 4 week (i.e., 28-day) period.
* Receiving a stable dose of one of the following AEDs: carbamazepine/oxcarbazepine, lamotrigine, levetiracetam or valproic acid. The AED dose must be stable 4 weeks prior to start of collection of baseline seizure data (retrospective or prospective) and during the Baseline period.
* Is able and willing to maintain an accurate and complete daily written seizure calendar and functional status diary or has a caregiver who is able and willing to do so for the entire duration of the study.
* Is able to comply with dosing of study drug, background AED and all study procedures.
* Has given written informed consent, or has a legally authorized representative who has given written informed consent, prior to the performance of any study assessments.
* A female subject is eligible to enter and participate in the study if she is either of non-childbearing potential or child-bearing potential but has a negative pregnancy test at Screening and agrees to satisfy one of the contraception methods as listed in the protocol, and is not pregnant or lactating or planning to become pregnant during the study.
* French subjects only: In France, a subject will be eligible for inclusion in this study only if either affiliated to or a beneficiary of a social security category.

Exclusion Criteria:

* Has a history of generalised epilepsy (e.g. Lennox-Gastaut, Juvenile Myoclonic etc.)
* Has had status epilepticus (other than simple partial status epilepticus) within the 24 weeks prior to Baseline Visit.
* Has participated in a previous retigabine study (subjects with documented evidence of having received placebo will be eligible).
* Is currently or has been abusing substance(s) or other medications in the 12 months prior to Baseline visit.
* Has taken an investigational drug, or used an investigational device, within the previous 30 days prior to screening or plans to take an investigational drug anytime during the study.
* Is currently following or planning to follow the ketogenic diet.
* Has been treated with vigabatrin within the past 6 months prior to collection of baseline seizure data.
* Is planning surgery or implantation of a Vagus Nerve Stimulator (VNS) to control seizures during the study.
* Is suffering from acute or progressive neurological disease, severe psychiatric disease, or severe mental abnormalities that are likely to interfere with the objectives of the study.
* Has any medical condition that, in the investigator's judgment, is considered to be clinically significant and could potentially affect subject safety or study outcome.
* Has a QTc ≥450 millisecond (msec) or greater than or equal to 480 msec for subjects with Bundle Branch Block at the time of screening.
* Has active suicidal plan/intent or has had active suicidal thoughts in the past 6 months. Has history of suicide attempt in the last 2 years or more than 1 lifetime suicide attempt.
* French Subjects: the French subject has participated in any study using an investigational drug during the previous 30 days or 5 half-lives (whichever is longer).