Documents released ahead of a US regulatory panel meeting for Vivus' Qnexa suggest that the obesity treatment may once again not be recommended for approval.

Papers have been published on the website of the US Food and Drug Administration ahead of a meeting of its Endocrinologic and Metabolic Drugs Advisory Committee on Wednesday (February 22) which will evaluate Qnexa (phentermine/topiramate). The agency issued a complete response letter for the drug in October 2010, citing concerns about potential side effects such as depression, memory loss, increased heart rate and birth defects.

In the briefing documents, the FDA staffers acknowledged that Qnexa can lead to significant weight loss, at least after the first year of treatment. Indeed, Vivus states that “the ability of Qnexa to produce durable weight loss can be expected to contribute significantly toward ameliorating some of the consequences of obesity and weight-related comorbidities”.

However, the FDA staff are not convinced, saying that "over all, the long-term clinical impact of the observed modest improvements in comorbidity outcomes is uncertain, particularly in a population with higher risk of cardiovascular adverse events". They also noted that latest studies show that use of topiramate during pregnancy increases the risk of oral clefts, eg cleft lips, by a factor of two to five.

Vivus has proposed labelling and other steps to ensure that women of "childbearing potential" would not use Qnexa, but the reviewers note that “the major consumers of weight-loss drugs are women of childbearing potential,” leading to “the potential for large numbers of pregnancy exposures".

Many analysts fear the worst and Simos Simeonidis at Cowen & Co expects a 'no' vote on Wednesday. He said "it's highly unlikely that the panel would recommend that a [cardiovascular outcomes] trial pre-approval is not needed".

He notes that the question as stated in the document of whether to approve Qnexa or not, is based on an un-restricted label (ie one that includes women of child-bearing potential). "Given that the teratogenicity issue seems far from being 100% resolved, we do not believe the vote to approve the drug, based on the proposed label, would be a positive one", Mr Simeonidis states. __