 This is a Phase IV adjunctive treatment dose-optimization study evaluating the efficacy, safety, and health outcomes of ezogabineretigabine immediate release IR GW582892 compared with placebo in adult subjects with partial-onset seizures POS. This randomized, double-blind, placebo-controlled, parallel-group, multicenter study will compare ezogabineretigabine IR investigator-selected daily doses of 600 milligram mgday, 750 mgday, 900 mgday, 1050 mgday or 1200 mgday with placebo. Study drug will be taken three times a day TID in equally or unequally divided doses. 