SAN FRANCISCO, Dec. 13, 2011 /PRNewswire/ -- Nektar Therapeutics (Nasdaq: NKTR) today announced positive data from a Phase 1 clinical study of NKTR-181 evaluating multiple ascending oral doses of NKTR-181 over an 8-day treatment period in healthy subjects. NKTR-181 is Nektar's new oral opioid analgesic candidate designed to address the abuse liability and serious central nervous system (CNS) side effects associated with current opioid therapies. In this multiple dose Phase 1 study, NKTR-181 exhibited a sustained analgesic response, supporting its development as a twice-daily oral tablet for the treatment of chronic pain conditions. Pupillometry data from the study demonstrated that NKTR-181's centrally-mediated opioid effects are dose-dependent and that the molecule enters the brain slowly, which could reduce the euphoria and other CNS side effects that are associated with current opioids. NKTR-181 was also well-tolerated over the entire 8-day dosing period in the study at all doses evaluated. NKTR-181 is a novel mu-opioid agonist molecule created using Nektar's proprietary polymer conjugate technology and its differentiating properties are inherent to the design of the new molecule. As a new molecular structure, NKTR-181 is unique in that it does not rely on a formulation approach to prevent its conversion into a more abusable form of an opioid. "NKTR-181 is emerging as an exciting new development in the treatment of chronic pain," said Lynn R. Webster, MD, Medical Director of Lifetree Clinical Research. "The positive findings from both of the Phase 1 studies for NKTR-181 demonstrate that NKTR-181 has a unique and highly attractive therapeutic profile that is inherent to its new molecular structure. As a novel opioid that could provide sustained analgesia with less CNS side effects and euphoria than existing opioids, NKTR-181 provides great promise for pain practitioners and for patients." In the Phase 1 multiple ascending dose study, NKTR-181 produced a dose-dependent and sustained analgesic response in a model of pain used in healthy subjects to measure central analgesic activity. NKTR-181 exhibited predictable dose-linear pharmacokinetics across all dose levels with an average half-life of approximately 12 hours and no evidence of pharmacological tolerance over the 8 days of twice-daily dosing. The sustained central response, analgesic effect and safety profile over a 12-hour period supports a twice-daily (BID) dosing schedule.