FDA Reconsiders Weight Loss Drug Qnexa

FDA Reconsiders Weight Loss Drug Qnexa
Weight Loss Impressive, but Safety Questions Remain

By Salynn Boyles
WebMD Health News

Reviewed by Laura J. Martin, MD

Nov. 9, 2011 -- The FDA is again considering approval of an experimental weight loss drug it rejected a year ago over concerns about potential heart problems and birth defects in babies born to women who take the drug.

California-based pharmaceutical company Vivus Inc, is now asking for limited approval for its oral combination drug Qnexa, which would exclude women in their childbearing years.

According to the company, the FDA is scheduled to make an approval decision next April. If approved, the drug could be commercially available soon after that.

That would make Qnexa the only prescription appetite suppressant approved for long-term use available in the U.S. The only other widely marketed prescription weight loss drug, orlistat -- sold by prescription as Xenical and over-the-counter as Alli -- works by blocking dietary fat absorption.

In a study submitted to the FDA last year in Vivus' original filing, and published in the journal Obesity late last week, people who took the highest dosage of Qnexa for a year lost, on average, about 14% of their body weight. They showed improvements in blood pressure, cholesterol, triglycerides, and blood sugar.

Qnexa Combines Two Drugs

Qnexa combines low doses of the stimulant phentermine -- long used for short-term weight loss -- and the anti-seizure and migraine drug topiramate, which has also been used "off label" to treat binge eating. "Off label" refers to drugs that are prescribed by doctors as treatments for conditions that are not specifically approved by the FDA.

Last fall, an FDA panel voted against the drug's approval, citing North American drug registry data showing that babies born to women who took topiramate had up to a 20-fold increase in cleft palates.

Vivus Inc. president Peter Tam tells WebMD that subsequent investigations involving other databases suggest that the risk for the oral birth defect is actually much lower.

Based on the new information, the FDA agreed to let the company resubmit its application for limited approval for use in adults who are not likely to become pregnant.

At the request of the FDA, the company is also examining more than a decade of medical claims records involving women who took topiramate during pregnancy to treat seizures, migraines, and other conditions, Tam says.

'Most Effective Drug Since Fen-Phen'

The newly published study included 1,267 severely obese people treated at 91 sites across the country.

Study participants took one of two doses of Qnexa or a placebo once a day during the year-long study. All were advised to follow a modest lifestyle modification/weight loss program that included counseling and a 500 calorie-a-day reduction, increased water intake, and increased physical activity.

Fifty-three percent of the placebo-treated patients remained in the study for the entire year, compared to 61% of the lower-dose Qnexa-treated patients and 66% of the higher-dose patients.

The most commonly reported side effects were tingling, dry mouth, constipation, and a tinny taste in the mouth.

At the end of the study, average heart rate increased by one beat per minute in the higher-dose Qnexa-treated patients and by less than one beat per minute in the lower-dose patients.

Diabetes specialist and study co-researcher W. Timothy Garvey, MD, of the University of Alabama at Birmingham, says based on the research Qnexa appears to be the most effective weight loss drug since the Fen-Phen weight loss regimen. Fen-phen was a combination of two separate drugs -- fenfluramine and phentermine. Fenfluramine, which was linked to potentially fatal heart problems, was pulled from the market in the late 1990s.

Among patients who completed the study:

The average weight loss for patients on the higher dose of Qnexa was 14.4% of body weight, compared to 6.7% among patients on the lower dose and 2.1% among patients taking a placebo.
48% of those in the higher-dose group lost 15% or more of their body weight, compared to 12% in the lower-dose group and 6% in the placebo group.
Sixteen percent of patients treated with the highest dose of the experimental combination drug dropped out of the study early because of the side effects, compared to 11% of patients in the lower-dose group and 8.4% of people who got the placebo treatments.

Tam says he is optimistic that Qnexa will be approved. But he acknowledges that the regulatory climate for weight loss drugs has been stormy of late.

Last October, in the same month that the first Qnexa application was rejected, the FDA also rejected Arena Pharmaceuticals' application for its weight loss drug lorcaserin for safety reasons . The agency also forced the withdrawal of the diet drug Meridia from the market after 13 years, citing concerns about heart attack and stroke risk.

Weight loss specialist Louis Aronne, MD, of Weill Medical College at Cornell University, says the FDA may feel pressure to approve Qnexa because it is effective, as long as the company shows that it can limit its use to those for whom it is approved.

Aronne directs the Comprehensive Weight Control Program at New York-Presbyterian Hospital.

"Obesity is a huge and growing medical problem and we need effective drugs to treat it," he tells WebMD.

He says just as weight loss surgery is now considered more of a medical than cosmetic procedure, a new generation of weight loss drugs will be thought of in the same way.

"This is not a cosmetic issue, it is a medical one," he says. "Weight loss has all kinds of health benefits, including improving blood pressure, diabetes, sleep apnea, and stroke and heart attack risk."

Bariatric surgeon Mitchell Roslin, MD, agrees, but he tells WebMD that his concerns about Qnexa remain. Roslin is chief of obesity surgery at Lenox Hill Hospital in New York City.

"We don't know if this drug is safe enough for patients to stay on it to maintain their weight loss," he says. "It clearly works better than other drugs out there, but the questions remain -- at what cost and for how long?"