Documents released ahead of a US regulatory panel meeting on Thursday suggest the chances of Vivus’ Qnexa becoming the first weight loss drug to be approved in the USA in over a decade look pretty good.

Papers have been published on the website of the US Food and Drug Administration ahead of a meeting of its Endocrinologic & Metabolic Drugs Advisory Committee on July 15 which will evaluate Qnexa (phentermine/topiramate). Vivus hopes the combo will be approved as an adjunct to diet and exercise for weight management in obese patients.

According to FDA staffers, efficacy is not a problem, as they noted that data from two Phase III trials showed that patients treated with low, medium and high doses of Qnexa lost 3%, 7% and 9% of their body weight, respectively. In these treatment arms, 45%, 62% and 69% lost more than 5% of their body weight, compared to 20% of those on placebo.

However, the problem for Vivus could lie in Qnexa’s safety profile. The staffers noted "five areas of particular interest," including cardiovascular events, effects on pregnancy, metabolic acidosis, plus cognitive-and psychiatric-related adverse events. Qnexa consists of the appetite suppressant phentermine, a component of the controversial ‘fen-phen’ diet pill (along with fenfluramine) which was withdrawn in 1997 after it was linked to potentially fatal heart valve complications. The other ingredient, topiramate, is an epilepsy drug sold before it recently went off-patent by Johnson & Johnson’s Topamax.

Despite the risks, analysts believe there is a good chance that the FDA panel will back Qnexa and investors seem to think so too. Vivus shares ended the day up 16.8% at $12.44.

The potential for an effective diet pill in the USA is enormous as figures suggest that over two-thirds of the population are obese. The FDA is expected to make its final decision by October 28.

Later this year, the agency is also planning reviews for two possible competitors to Qnexa – Arena Pharmaceuticals’ lorcaserin and Orexigen Therapeutics’ Contrave (bupropion/naltrexone.)