The FDA has finally approved Entereg to treat post-operative ileus, or POI, a gastrointestinal disorder that is common after bowel resection surgery, and is marked by stomach bloating, pain, nausea, and constipation. This is a relief for Glaxo and Adolor, because FDA approval was slow in coming.

The move comes four months after an FDA panel voted that the benefits outweigh the risks to the heart. The FDA held up development last year after a large one-year study testing it for a different chronic bowel condition found an increased number of heart attacks, bone fractures and some cancers. The drug was previously delayed when the FDA asked the companies to produce more clinical data.

There are caveats, though, as David Amsellem, an analyst at Friedman Billings Ramsey, points out in an investor note this morning. Entereg will be available under a restrictive risk management program designed to mitigate CV events, which “puts the brakes on off-label use, limiting sales potential.” This will make usage “onerous for doctors, and likely limit usage to patients who are not recovering gastrointestinal function several days after surgery,” he writes. His sales forecast: $92 million 2012.

There’s also a boxed warning for short-term hospital use and it will be contraindicated in patients who have taken therapeutic doses of opioids for more than seven consecutive days prior to usage.

He notes the drugmakers “did not address the clinical hold on the development program in opioid-induced bowel dysfunction, which we take to mean that the hold in this program remains in force. Given that cardiac safety signal seen in the OBD program and the high safety hurdle that will surely characterize any future studies, we find it difficult to envision the OBD indication as commercially viable.”