Lacosamide is a functionalized amino acid, the antiepileptic effects of which appear to be due to a novel mode of action, namely the selective enhancement of slow inactivation of voltage-gated sodium channels. Lacosamide is available as oral or intravenous formulations. Bioequivalence between the oral tablet and the oral syrup of lacosamide has been established. The bioavailability of the oral lacosamide tablet was similar to that of a 30- or 60-minute intravenous infusion of lacosamide administered at the same dosage. Oral lacosamide when added concomitantly with between one and three antiepileptic drugs was effective in adult patients with uncontrolled partial-onset seizures with or without secondary generalization, according to pooled data (n = 1308) from three phase II/III studies that had a 12-week maintenance phase. The percentage of patients with a >or=50% reduction from baseline to the maintenance phase in seizure frequency was significantly greater with oral lacosamide 200 or 400 mg/day (34% and 40%) than with placebo (23%). The median percentage reduction in seizure frequency per 28 days from baseline to the maintenance phase was significantly greater with lacosamide 400 mg/day than with placebo in each of the three phase II/III studies. Lacosamide was generally well tolerated in adult patients with partial-onset seizures, with most treatment-emergent adverse events being of mild or moderate severity. Dizziness was the most common treatment-related adverse event. When used as short-term replacement for oral lacosamide, intravenous lacosamide was well tolerated when administered as a 15-, 30- or 60-minute infusion.