• The primary objectives of this placebo-controlled clinical trial are to evaluate the analgesic efficacy and safety of bicifadine 200 mg BID compared with placebo in patients with moderate to severe chronic low back pain.
• The secondary objectives are to evaluate the effect of bicifadine on function and general quality of life, to evaluate safety following discontinuation of bicifadine treatment and to investigate the population pharmacokinetics of bicifadine.

Main Inclusion Criteria:

• Patients with low back pain assessed as Class 1, Class 2 or Class 3 according to the Quebec Task Force Classification for Spinal Disorders and without detectable leg weakness on neurological examination.
• Patients with pain categorized as Class 1 according to the Quebec Task Force Classification must have a Roland-Morris Disability Rating of >17 at baseline to qualify. Patients with pain categorized as Class 2 or Class 3 according to the Quebec Task Force Classification must have a Roland-Morris Disability Rating of at least 10 at baseline to qualify.
• Patients must have required daily analgesics for the treatment of low back pain for at least 3 months prior dosing.

Main Exclusion Criteria:

• Patients may not have persistent moderate or severe pain in a location other than the lower back (with the exception of radiation to the lower extremity).
• Patients must not have had lower back surgery within 6 months prior to baseline, nor epidural corticosteroid injections within 3 months prior to baseline.
• Patients may not have an unstable medical condition.