NOVELTY - An extended release pharmaceutical composition (C1) of lacosamide or its salts comprises at least one rate-controlling polymer and at least one excipient.    USE - As an extended release pharmaceutical composition of lacosamide for treating partial onset seizures in patients with epilepsy and preventing visual disturbance or P-R (time between the start of arterial systole and start of ventricular systole) prolongation (claimed). Also useful as anticonvulsant drug in the treatment of central nervous system disorders such as epilepsy; pain, particularly neuropathic pain such as diabetic neuropathic pain.    ADVANTAGE - The composition retains at least 80% of the potency of lacosamide or its salts after storage for 3 months at 40 degrees C/75% relative humidity (RH); exhibits a dissolution profile of lacosamide or its salts such that at least 80% of lacosamide or its salt is released from 8-24 hours after administration; exhibits no significant difference in both rate and extent of absorption of lacosamide or its salt as compared to Vimpat (RTM: immediate release formulation of lacosamide) administered twice daily; and exhibits a dissolution profile of lacosamide or its salts in water or simulated gastric fluid such that at least 10% of lacosamide is released after 2 hours, at least 20% of lacosamide is released after 4 hours, at least 40% of lacosamide is released after 8 hours, at least 60% lacosamide is released after 10 hours, and at least 80% lacosamide is released within 24 hours. The composition provides extended therapeutically effective plasma levels over a twenty four hour period with reduced incidences of neuropsychiatric side effects. The composition is easy and inexpensive to manufacture and convenient for the patient to use; prevents peak-trough fluctuations in plasma levels and thus maintains therapeutically effective plasma levels of lacosamide over an extended period of time; and allows for a reduced frequency of dosing e.g. once a day dosing, and thus improves patient compliance.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparing an extended release pharmaceutical composition (C1) involving mixing lacosamide or its salts with at least one rate-controlling polymer optionally with other excipient and forming the mixture thus obtained into pharmaceutical dosage form; and optionally granulating or compression molding of above mixture to form granules, pellets, tablets and minitablets.