ObjectivesTo evaluate the efficacy and safety of lacosamide (200mg/d and 400mg/d)when added to 1 to 3 antiepileptic drugs (AEDs) in adults with uncontrolled partial-onset seizures. MethodsDuring this multicenter, double-blind, placebo-controlled trial, patients were randomized to placebo or lacosamide 200 or 400mg/day after an 8-week baseline period. Lacosamide was titrated in weekly increments to target dose over 4 weeks and maintained for 12 weeks followed by 12 weeks for withdrawal. The reductions of seizure frequence during maintain period and proportion of ≥50% reduction of seizures frequence were analysed. Besides,adverse effects were also recorded. ResultsFive hundred fourty patients were randomized, 515 patients completed the trial (Full analysis set, FAS), including 394 were per-protocol set (PPS). The reduction of seizure frequence during maintain period every 4 weeks among 200mg/d,400mg/d group and placebo group were 26.35%,40.12%,21.69%(P=0.000 5) and 25.61%,46.86%,23.06%(P<0.000 1), respectively in FAS and PPS. The proportion of ≥50% reduction of seizures frequence among three groups were 29.82%,38.15%,22.49%(P=0.006 8) and 27.94%,42.37%,22.86%(P=0.002 3), respectively in FAS and PPS. The incidences of adverse events were 5.84%, 36.11%, 19.55% among three groups. Compared with each other, there was statistic significance between 400mg/d and placebo groups. ConclusionIn this trial, adjunctive lacosamide significantly reduced seizure frequency in patients with uncontrolled partial-onset seizures. Along with favorable pharmacokinetic and tolerability profiles, these results support further development of lacosamide as an AED.