The purpose of this study is to determine the efficacy and safety of EN3324 (axomadol) in subjects with moderate to severe chronic low back pain

A phase IIB, randomized, double-blind, two-arm, multi-center, placebo-controlled, study to assess the efficacy and safety of EN3324 (axomadol) in subjects with moderate to severe chronic low back pain

Inclusion Criteria:

• 18 years of age or older
• Are females who are participating abstinence or using a medically acceptable form of contraception or have been post-menopausal, biologically sterile, or surgically sterile for more than 1 year.
• Have been on an unchanged regimen of analgesic medication for chronic low back pain on a daily basis for at least 3 months prior to screening; subjects taking opioids must not exceed total daily doses of 90mg oral morphine equivalent
• Have a history of moderate to severe CLBP

Exclusion Criteria:

• Have evidence of or a history of alcohol and/or drug abuse
• Have pain secondary to a confirmed or suspected neoplasm
• Intend to alter their physical therapy regimen during the study. Subjects who begin or end physical therapy (either home exercises or formal therapy sessions) 2 weeks prior to screening or during the study period will be excluded from the study
• Have a history or physical examination finding, which may confound pain-related data (e.g., fibromyalgia, radiculopathy)