MOUNTAIN VIEW, Calif. ( TheStreet) -- In a review posted to its Web site Tuesday, U.S. drug regulators said Vivus' ( VVUS) weight-loss drug Qnexa was effective in helping obese patients shed pounds, but the agency raised questions -- most of them expected -- about the drug's safety.

Vivus shares were up about 34% to $14.25 in Tuesday's pre-market trading session as anxious investors breathed a sigh of relief over the U.S. Food and Drug Administration's relatively benign review of Qnexa, which didn't yield any "Uh Oh!" revelations about the drug's safety.

The FDA will convene an outside panel of experts Thursday -- which TheStreet will be covering via live blog -- to review Vivus' approval application for the weight-loss drug Qnexa. Vivus is trying to become the first company in more than a decade to gain U.S. approval for a new weight-loss drug. Two other companies -- Arena Pharmaceuticals ( ARNA) and Orexigen Therapeutics ( OREX) -- are fast on its heels.

In the FDA's review of Qnexa, posted online Tuesday as part of the briefing documents for Thursday's advisory panel, pooled data from two large phase III studies demonstrated that patients treated with low, medium and high doses Qnexa lost between 3 percent, 7 percent and 9 percent of their body weight, respectively, adjusted for the weight-loss reported for patients treated with a placebo.

Twenty percent of placebo-treated patients lost more than 5% of their body weight, compared to 45 percent, 62 percent and 69 percent of Qnexa patients.

According to the efficacy criteria laid out by FDA for weight-loss drugs in 2007, the FDA concluded that, "all three doses of PHEN/TPM Qnexa were efficacious for weight loss."

Qnexa's safety and not the drug's ability to help patients lose weight, was the major concern entering Thursday's meeting. In its briefing document Tuesday, FDA's safety review highlights five areas of "particular interest" related to Qnexa -- pregnancy risk, psychiatric-related adverse events, cognitive-related adverse events, metabolic acidosis and cardiovascular events.

All of these safety issues had been anticipated by investors as major areas of discussion at Thursday's panel. The FDA chose not to state its own opinion of Qnexa's overall safety in Tuesday's review documents.

"The FDA's briefing documents contained no smoking guns," related to Qnexa's safety, said JMP Securities analyst Jason Butler. He has an outperform rating on Vivus with an $18 price target.

Vivus' Qnexa consists of two currently approved drug: The generic weight-loss drug phentermine and topirimate, a drug used to treat epilepsy and migraine, marketed as Topomax by Johnson & Johnson ( JNJ).

-- Reported by Adam Feuerstein in Boston.

Follow Adam Feuerstein on Twitter.
Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

If you liked this article you might like

Goodbye

Goodbye CytRx, Your Game Is Over

Juno Therapeutics Mounts CAR-T Comeback With Strong Lymphoma Study Results

Bluebird, Celgene CAR-T Keeps Multiple Myeloma Patients Relapse Free

'APHINITY' Study Spells Major Trouble for Roche, Another Win for Puma Bio