Drugmaker Adolor (Nasdaq: ADLR) got a bit of surprising good news from the FDA on Friday, only a few weeks ahead of an upcoming FDA decision on whether to approve the company's lead drug.

The good news came in the form of a briefing document that the FDA released. In the document, which was released prior to the upcoming advisory panel discussion on Adolor's potential post-operative ileus (POI) treatment, Entereg, the agency gave what appeared to be a relatively positive review.

POI is a condition best described as constipation that occurs following abdominal surgery. For patients who have just had major surgical work on their bowels, it can be a serious and painful side effect and can prolong post-surgery hospital stays.

Adolor has been trying to get Entereg approved to treat POI since 2005, and has already received two approvable letters for the drug. The first approvable letter from the FDA came in 2005, asking for more efficacy data, and the second approvable letter, in 2006, was a result of some cardiovascular safety issues that occurred in an opioid-induced constipation study by Adolor partner GlaxoSmithKline (NYSE: GSK).

Despite a lack of resolution to the cardiovascular issues, as well as some worrisome new issues that popped up in the drug's long-term use, Adolor went ahead and filed for a third FDA review for Entereg last year. Tomorrow's advisory panel hearing and the Feb. 10 PDUFA date are the results of this third attempt at getting Entereg approved.

In the briefing documents (PDF) posted by the FDA's gastrointestinal review division ahead of the advisory committee hearing, the agency appears ready to approve Entereg to treat POI if it can prevent off-label usage of the drug. The FDA review team seemed satisfied that Entereg worked, noting the "positive efficacy results across several studies," and seemed relatively satisfied that the multiple safety issues that have popped up after the long-term use of Entereg may not be an issue in short-term POI use.

The biggest sticking point holding up approval of Entereg is that the FDA's gastrointestinal review team doesn't want Entereg prescribed off-label or outside the hospital. Almost all the safety questions asked by the FDA review team for the advisory panel were related to these issues:

Regarding safety, we are interested in the Committee's opinion regarding the short-term use of (Entereg). Are there safety concerns? Will the potential cardiovascular risk be minimized sufficiently by the proposed Risk Management Plan? Can longer term use and outpatient use of (Entereg) be prevented by limiting sales by wholesaler to hospitals only? What other aspects of such a plan need to be included?

Any chance of future Entereg approval for opioid-induced constipation looks dead in the water, so rivals Progenics Pharmaceuticals (Nasdaq: PGNX) and Wyeth (NYSE: WYE) will likely have that market to themselves if the FDA approves their competing drug when their April 30 PDUFA date comes up.

Previously, I thought Entereg's chances with the FDA were minimal in POI. On balance, the briefing docs seem to signal that approval to treat POI may be on the way, but with a very restrictive label that will not allow for any off-label usage of the drug in other indications. I probably don't need to say, though, that marketing approval is never a sure thing when it comes to the FDA. The agency still has a few Entereg safety-related questions to mull, but if the advisory panel can help come up with answers to further appease the FDA review team, then it looks like Entereg regulatory approval will occur either outright or after a short approvable letter.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. GlaxoSmithKline is an active Income Investor pick. The Fool has an A+ disclosure policy.