An FDA review of closely watched prescription obesity drug Qnexa ended in disappointment for its developer, Vivus, as concerns about a lack of long-term safety data led experts to recommend against the drug’s approval. The news delivered a drubbing to Vivus’ stock, which fell more than 60 percent following the vote, wiping out more than $500 million in market cap for the company.

The FDA's Endocrinologic and Metabolic Drugs Advisory Committee split, with 6 members recommending approval of Qnexa and 10 recommending against approval, according to reports. The agency almost always follows the committee's recommendation, although Vivus holds out hope that it may not in this case.

Vivus CEO Leland Wilson says the company is disappointed in the vote, yet encouraged that the committee recognized the efficacy of Qnexa in trials.

“We are not deterred,” Wilson told investors on a brief conference call following the vote.

"We will work closely with the FDA leading up to our October 28, 2010 PDUFA date to address the labeling and safety questions raised during today's proceedings. We remain committed to patients living with obesity and weight-related disease," Wilson says.

In background documents filed before the meeting, reviewers cited concerns about the effects of Qnexa during pregnancy, and psychiatric-related adverse events, cognitive-related adverse events, metabolic acidosis, and cardiovascular events.

The review of Qnexa has been scrutinized as not just important for Vivus, but as a bellwether for how the agency will evaluate two other obesity treatments in line for review this year. The same optimistic investors driving up the value of Vivus shares before the panel review also drove up share values for the next contestants, Arena Pharmaceuticals and Orexigen before the vote. Shares of the later two companies fell following the vote. Shares of Vivus were temporarily halted during the review.