This phase 2b trial is being conducted at approximately 60 sites in the US to investigate whether lacosamide (SPM 927) at different doses reduces pain in subjects with diabetic neuropathy. Approximately 360 subjects will be randomized to placebo or one of three doses of lacosamide. To qualify for this trial, subjects with symptoms of painful distal diabetic neuropathy ranging in duration from 6 months to 5 years must have an average pain intensity of ≥4 on an 11-point Likert scale (0-10 scale) during the 7 day period prior to start of treatment.

To determine what effect lacosamide has on diabetic neuropathic pain, subjects will use a diary to record their daily pain intensity (morning and evening), pain interference with sleep (morning) and activity (evening). Use of rescue medication (acetaminophen) and subjects' quality of life will be investigated. In addition, safety and tolerability of the different doses of lacosamide will be investigated.

Inclusion Criteria:

• Painful distal diabetic neuropathy

Exclusion Criteria:

• Must have an average pain intensity of ≥ 4 on an 11-point Likert scale