The purpose of this 52-week open label study is to determine the long-term safety of a new opioid molecule, NKTR-181, in patients with moderate to severe chronic low back pain or chronic non-cancer pain.

This is an open-label safety and tolerability study in which approximately 600 subjects will receive NKTR-181 for up to 52 weeks. Subjects may include newly enrolled subjects and subjects who have recently completed SUMMIT-07 study.

This study will also investigate the pharmacokinetics of NKTR-181 in patients 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