Long-Term Safety and Tolerability Study of NKTR-181 in Subjects With Chronic Low Back Pain or Chronic Non-Cancer Pain

Inclusion Criteria: * Male or non-pregnant, non-nursing female aged 18 to 75 years old * Clinical diagnosis of moderate to severe, chronic low back or non-cancer pain for at least three months * Not experiencing adequate pain relief or have failed previous treatment with non-opioid analgesics * Opioid analgesia is necessary * Currently taking no less than 10 mg but no more than 60 mg of morphine sulfate equivalents (MSE) per day of opioid analgesics for at least 7 days prior to entry * Females of child bearing potential must be using a highly effective form of birth control. All subjects must agree to use double-barrier contraception during participation in this study and for at least 2 months after the last dose of the study drug. * Willing and able to provide informed consent Exclusion Criteria: * History of hypersensitivity, intolerance, or allergy to opioids * Surgical procedures in the last 4 weeks or plans to undergo surgical procedures during the study period * Untreated moderate to severe sleep apnea * Chronic migraines as the primary pain condition * Cancer related pain