Adolor said the Food and Drug Administration will not issue an "action letter" by tomorrow, which had been the expected decision date. The FDA told the company it expects to issue the action letter "shortly."

Adolor shares fell 10 cents, or 2 percent, to $4.69 in midday Nasdaq trading.

FDA approval to sell Entereg, also called alvimopan, is a crucial hurdle. Adolor has no marketed products and has worked seven years developing the drug with partner GlaxoSmithKline P.L.C.

It was the second delay. The FDA was originally expected to decide in February. In January, an FDA advisory panel voted 9-6 that the benefits of Entereg outweighed potential risks, including heart attacks, bone fractures and tumors observed in one longer-term study.

But FDA advisors also said the company's proposed risk-management plan to monitor the drug was inadequate, and they expressed concern about long-term cardiovascular risks. In February, Adolor submitted a revised plan to monitor use of the drug.

Entereg is a treatment for post-operative ileus, a gastrointestinal condition that can occur after bowel surgery.

The FDA panel said the drug worked and reduced hospital recovery time by about a day after abdominal surgery, but expressed concern that Entereg not be prescribed outside of hospitals and be given to patients only short-term.

Adolor and GlaxoSmithKline are proposing that Entereg be used by patients up to seven days, and only before and after bowel surgery, to prevent constipation and nausea associated with taking narcotic painkillers, such as morphine.

Founded in 1993, Adolor has already received two "approvable" letters for Entereg. But cardiovascular issues emerged last year after a longer opioid-induced constipation study uncovered serious side effects in patients taking Entereg for six to 12 months.

In April 2007, after Adolor and GlaxoSmithKline halted the study, Adolor's stock plunged 59 percent.