Once rejected by the FDA over safety concerns, the weight loss pill Qnexa on Wednesday will get a second chance before an FDA advisory committee.

Will the second time around be the charm? Qnexa maker Vivus Inc. hopes so. And the company will be showing off new safety data from patients who took Qnexa for a second year after completing a one-year clinical trial.

Whether that will sway the panel -- and, ultimately, the FDA -- is a tough call.

Qnexa combines two currently approved drugs. One is the appetite suppressant phentermine, the safer "phen" part of the infamously unsafe fen-phen diet drug.

The other half of Qnexa is the seizure/migraine drug topiramate. The topiramate label lists some scary side effects: eye problems, decreased sweating and increased body temperature, acidic body fluids, suicidalthoughts and behaviors, and fetal toxicity.

But Vivus' new data suggests that the FDA's main safety concerns, heart risk and birth defects, were not a big issue in the follow-up study. Neither were worries about increased suicide risk, mental dulling, or too much acid in body fluids.

These may not have been major issues in the clinical trials, but troubling safety issues persist. In the FDA's analysis of Qnexa safety, there were some ominous comments:

• There was indeed evidence of increased heart rate and acidic body fluids in people taking Qnexa.
• The FDA states that "only a long-term" study can tell whether Qnexa increases the risk of heart diseasein obese people already at high heart risk. One question before the panel is whether Vivus must conduct such a study.
• A disturbing number of women in the clinical trials got pregnant, even though they had agreed to be onbirth control and had regular pregnancy checks. One of the ingredients in Qnexa is linked to birth defects, although none were seen in the clinical trial. Since 36% of U.S. women are obese, the FDA worries that a lot of pregnant women will be exposed to Qnexa.

Does Qnexa Benefit Outweigh Qnexa Risk?

While the argument over Qnexa approval isn't about efficacy, not everyone taking the drug loses a significant amount of weight:

• On average, people taking the dose of Qnexa proposed for approval lost 6.6% of their body weight. For approval, the FDA requires that a drug result in average loss of at least 5% of body weight.
• In one study, 62% of obese and overweight people taking Qnexa lost at least 5% of their body weight -- about three times as many as in the placebo group. The FDA standard is that 35% of people must lose 5% of body weight.
• In a follow-up study, people continuing to take Qnexa for a second year regained some of the weight they lost the first year. They did not regain as much weight as people taking a placebo.

Since Qnexa exceeds the FDA's minimum effectiveness requirement, the question is whether the new safety data will sway the new FDA panel.

The last panel voted 10 to 6 against approval. But a lot of those voting said it was a close call.

This year, there are 22 panel members scheduled to vote. Twelve of them were on the last panel. Last time, seven of them voted "no" to approval, and five voted "yes."

SOURCES:FDA web site.FDA briefing document, Feb. 22 meeting of the Endocrinologic and Metabolic Drugs Advisory Committee.