* Qnexa helped patients lose weight
* One ingredient tied to birth defects
* Uncertain effect on the heart
* FDA advisory panel to vote on drug Wednesday afternoon
* Vivus shares halted pending vote
By Anna Yukhananov
SILVER SPRING, Md., Feb 22 (Reuters) - Proponents of a new obesity medication from Vivus Inc told U.S. reviewers on Wednesday that the drug's health benefits exceed heart and birth defect risks.
A panel of outside experts to the Food and Drug Administration will vote later on Wednesday on whether to recommend approval for what would be the first new prescribed drug for obesity in 13 years.
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.
Qnexa, which combines the appetite suppressant phentermine and anti-seizure drug topiramate, helped patients lose at least 10 percent of their weight after a year of treatment, the company said .
Obesity, a leading cause of diabetes, heart disease and other serious health problems, has reached epidemic proportions in the United States, with about a third of the population obese and more than half overweight.
"Back in medical school, I was taught that when the risk of not treating the condition exceeds the risk of treating it, we should treat," said Dr. Arya Sharma, a chair in obesity research at the University of Alberta in Canada and paid consultant to Vivus.
"We have an obligation to change how we measure obesity. Qnexa addresses an urgent and substantial unmet medical need for our patients," he told panelists.
The FDA has set a high approval bar for weight loss drugs because such a large portion of the general population is likely to want to take them, and has not approved a new obesity drug since 1999.
Also, many diet pills have been linked to serious heart-related risks.
But patient groups say the FDA is holding obesity drugs to a higher standard than other treatments because of views that it is a choice, not a disease. They are urging the FDA to approve new obesity drugs that would give patients another option between lifestyle changes and surgery.
Shares of Vivus were halted on Nasdaq on Wednesday pending the outcome of the FDA panel meeting. They closed at $10.55 on Tuesday, well above the stock's low around $4.70 after the pill was first rejected.
FDA staff presenting on Wednesday said the key issues with Qnexa were about safety, not efficacy.
Staff reviewers have said patients taking the drug had more safety problems, including memory loss and higher heart rates, than those on a placebo, and some of these problems could get worse over time.
They have also noted that exposure to one of the ingredients in Qnexa has been linked to a higher rate of birth defects.
A Vivus study showed topiramate caused a higher rate of oral clefts in infants of women taking the drug during pregnancy, and the company said it would limit Qnexa to women who are not pregnant.
The FDA has said the rate of potential birth defects is about two to five times higher with topiramate than with placebo.
Vivus officials said obesity, and its common symptom diabetes, come with their own risks to pregnancy, such as stillbirth, premature birth and other complications.
The FDA and the company generally agreed on a program to mitigate the drug's risks to pregnant women, including limiting the drug to certified pharmacies and training doctors who would prescribe it.
Panelists will discuss whether they think the program is stringent enough to protect patients from the risk of birth defects.
In clinical trials, Qnexa also increased patients' heartbeats, leading to fears it may have negative effects on the heart. However, Vivus said the drug also reduced blood pressure, and a link between heartbeat and heart health was not conclusive. (Reporting by Anna Yukhananov; Editing by Tim Dobbyn)