The primary objectives of this placebo-controlled clinical trial are to evaluate the analgesic efficacy and safety of bicifadine at three oral dose levels compared with placebo in patients with moderate to severe chronic low back pain.

The secondary objectives are to investigate the dose-response relationship of three dose levels of bicifadine, to evaluate the clinical meaningfulness of bicifadine efficacy, to evaluate the effect of bicifadine on function and general quality of life, to describe the population pharmacokinetics of bicifadine in patients with chronic low back pain, and to evaluate safety following discontinuation of bicifadine treatment.

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 must have required on average daily analgesics for the treatment of low back pain for at least 3 months prior to dosing.

Main Exclusion Criteria:

• Patients may not have 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.