AstraZeneca has begun enrollment of a late-stage trial for an investigational opioid-induced constipation treatment licensed from Nektar Therapeutics.

The drug, NKTR-118, is a once-daily tablet that combines Nektar's small molecule polymer conjugate technology platform with naloxol, a derivative of the opioid antagonist naloxone. It is being studied for OIC, a common side effect of prescription opioids used for chronic pain management.

AZ said for those patients who take opiates for long-term pain management, 40% to 50% will develop constipation. Only half of those experience effective relief from laxatives and stool softeners.

The first regulatory filings based on the program are planned for 2013. AstraZeneca and Nektar teamed up in September 2009; the deal includes the earlier-stage NKTR-119, which combines NKTR-118 and an opioid analgesic. When the pact was signed, AstraZeneca made a $125 million upfront payment. The deal could be worth $1.5 billion to Nektar.