This phase 2/3 open-label trial is being conducted at approximately 100 sites in the US to assess the safety and tolerability of long-term treatment with lacosamide (SPM 927) in subjects with painful diabetic neuropathy. Approximately 525 subjects will be enrolled. To qualify for this trial, subjects with symptoms of painful distal diabetic neuropathy ranging in duration from 6 months to 5 years must have completed trials SP665, SP742, or SP768 and, in the investigator's opinion, may benefit from long-term administration of lacosamide. Subjects will be titrated to their optimal dose of lacosamide (up to 600mg/day). The safety and tolerability of the different doses of lacosamide will be investigated throughout the trial. In addition, to determine what effect lacosamide has on diabetic neuropathic pain, subjects will use a diary to record their daily pain intensity and pain interference with sleep and activity. Subjects' quality of life will also be investigated.
