After a second review of its effectiveness and safety profile, Qnexa, an anti-obesity drug by Vivus Inc, has gained an FDA panel's approval and may soon become the first new prescription weight loss drug in the United States in 13 years.
“Of all the obesity drugs, this one has the highest efficacy in terms of weight loss, so that shifts the balance in terms of requiring a post-approval study rather than a pre- approval study,” said Sanjay Kaul, a cardiology professor at UCLA Cedar Sinai Medical Center and a member of the FDA’s Endocrinologic and Metabolic Drugs Advisory Committee who voted 20-2 in favor of the drug.
Qnexa combines two medications, phentermine and topiramate. Phentermine, also sold under several brand names such as Adipex, is in a class of medications known as anorectics. These drugs stimulate the hypothalamus gland (the region of the brain responsible for appetite) and affect certain neurotransmitters which ultimately suppress the appetite and lead the dieter to eat fewer calories.
Topiramate, also sold as Topamax, was originally approved as a medication that treats certain types of epileptic seizures and to prevent migraine headaches. It is also sometimes used in addiction therapy, such as the case of alcohol abuse. The drug may not only help provide a feeling of fullness and satiety, effectively reducing appetite, but may also be especially affective in those with binge-eating disorder.
In clinical trials, the drug has been found to be very effective for weight loss, however, the FDA originally voted to reject Qnexa last year because of concerns about an increased risk of heart ailments and birth defects. Side effects of phentermine include elevation of blood pressure and an increase in heart rate. The greater concern is the risk of birth defects in fetuses born to pregnant women who take topiramate.
Women who have taken topiramate during the first trimester of pregnancy have been found to have a prevalence rate of oral clefts (cleft lip) at about 0.29 percent or 5 in 1,000 live births. This is five times the overall rate of 1 in 1,000.
While weight loss is never suggested for a pregnant woman, many women aren’t aware of a pregnancy until sometime in the middle of the first trimester. By then, the fetus has already been exposed to the drug. Obese women in particular can have irregular menstrual cycles and may take longer to become aware of a pregnancy.
Vivus Inc, based in California, has proposed several options to the FDA in order to have Qnexa approved and used by only the most appropriate candidates. The company will conduct a post-approval trial to assess the risk of major heart complications that would involve over 11,000 patients over the next four and a half years. They will also maintain a patient database of those prescribed the drug and follow any babies born to those women.
The company has also proposed a black box warning label to advise physicians against prescribing the drug to women with the potential to become pregnant, although the FDA rejected this proposal on February 17th mainly because topiramate is also used for other conditions. Russell Katz, director of FDA’s neurology products division, said the agency hasn’t considered restricting the drug because there aren’t many options for migraine prevention.
Vivus has also suggested restricting distribution of Qnexa to less than 10 large mail-order pharmacies with pharmacists trained in dispensing the drug, Barbara Troupin, senior director of global medical affairs at the company, said. Patients would receive a medication guide that emphasizes contraceptive use while taking Qnexa.
The FDA is scheduled to make its final decision by April 17th. If approved, Qnexa, a once-daily medication for men and women with a body mass index (BMI) of 30 or greater, will be the first new prescription weight-loss treatment since the 1999 approval of Roche’s Xenical. Business Week reports that, if approved, the drug may generate $448 million in sales in 2015.
The potential for approval excites other pharmaceutical companies vying to get new weight loss drugs onto the market as the obesity epidemic continues to grow. According to statistics by the CDC, more than one-third of US adults are obese and another third are overweight. The obesity rate among adults has more than doubled since 1980 and costs the US economy an estimated $147 billion a year in medical expenses and lost productivity.