U.S. advisers back experimental obesity pill

Experimental obesity drug Qnexa won the backing of U.S. health advisors on Wednesday, raising hopes for approval of the first prescription weight-loss pill in 13 years.

Vivus Inc's Qnexa was one of three promising obesity drugs rejected by the U.S. Food and Drug Administration in the past two years over safety concerns.

It is the first to come back up for review after more extensive clinical trials, as public health officials urge the FDA to consider a medical treatment for a condition that affects about one-third of Americans.

A panel of outside experts to the FDA voted 20-2 to recommend approval of Qnexa, saying they were convinced that the benefits it offers in treating obesity outweighed the potential heart risks and birth defects associated with the drug.

Vivus shares nearly doubled in value to $21.01 in afterhours trade following the panel vote.

Qnexa®, produced by Vivus Inc, is a medication being studied for the treatment of obesity. Qnexa is an appetite suppressant and is a blend of two separate already existing medications Phentermine and Topiramate (brand name Topamax®). Phentermine has been approved by the FDA and has been used for many years as a very successful weight loss formula. Topiramate is a medication that has also been approved by the FDA and has been used for years as an anticonvulsant to treat epilepsy and has also been used to treat migraine headaches or as an antidepressant. However, it is the combination that is being tested and the results are promising. It is believed that Qnexa will greater reduce appetite and increase weight loss than Phentermine or Topiramate alone as well as show that it is a safer drug than either one substance by itself. Studies have shown that Qnexa has attained a larger weight loss compared to the placebo as well as compared to each of the two combined drugs individually. The FDA requires that in order for an obesity drug to be considered effective it must show that at least a third of the test patients lose at least 5% of their body weight. Qnexa passed this better than most.

Panelists did say Vivus should conduct a study on possible heart problems and supported the company's plan to limit its use to women who are not pregnant.

During discussions, panelists seemed divided on whether the heart-focused safety study should happen before or after the drug is approved. They took no formal vote on that issue. A pre-approval study could delay the time before Qnexa is available to patients.

Shares of fellow obesity drugmakers Orexigen Therapeutics and Arena Pharmaceuticals got a 17 percent boost in extended trading.

The FDA first rejected Vivus' Qnexa in 2010 because of safety problems, along with two other obesity pills that are also seeking a second round of consideration.

The FDA usually follows panel recommendations, although it is not required to. It will make a final decision by April 17.