Qnexa, a combination of phentermine and topiramate, is a proposed anti-obesity medication. Although clinical trials demonstrate that Qnexa can lead to an approximately 10% weight loss, an FDA advisory committee recommended against approval in 2010 because of safety concerns (an increased risk of cleft lip and palette and increased heart rate, which could increase the cardiovascular risk). On February 22, 2012, an FDA advisory committee voted 20-2 in favor of approval, based on an additional submission by the sponsor, Vivus Inc.
In a commentary in Annals of Internal Medicine, Michael Lauer of the National Heart, Lung, and Blood Institute explains why he voted against recommending approval. Briefly, he discusses how the small pre-approval trials conducted by the sponsor, and the small number (12) of major cardiovascular events that occurred during those trials, give us insufficient information to determine whether Qnexa increases the risk of cardiovascular events. Qnexa is thus like a used car that could be either a “lemon” or a “peach.” In addition, based on prior experiences with obesity medications that were withdrawn from the market due to cardiovascular effects, we have reason to be concerned about an obesity medication that increases heart rate (consider the case of Meridia, previously discussed on this blog here and here). Finally, the sponsor’s argument that certain improved biomarkers, such as blood pressure and high-sensitivity C-reactive protein, outweigh any effect of the increased heart rate, fails to assuage his concerns given the failure of surrogates in the past. He states that “We cannot assume that just because a drug reduces weight and improves some biomarkers that it will be safe, let alone beneficial.” I completely agree. Here is his conclusion, but his commentary is open access, so I urge you to read it in full:
So what to do? We can resolve the information asymmetry by insisting on a large-scale, preapproval cardiovascular outcomes trial of Qnexa. It would be too risky to rely on postapproval surveillance or to hope that a rigorous trial could be conducted in a timely manner. If Qnexa prevents cardiovascular events, or at least doesn’t increase the risk for them, in a preapproval trial, then we will all know that we have the peach we’ve been waiting for.