Why Vivus's Qnexa Might Not Avoid the Obesity Drug Graveyard

(MoneyWatch)  Many have tried. None have succeeded. And now Vivus -- a young Arthur of Pharmalot, if you will -- believes it can pull the sword from the stone. On paper, it has a good case. My colleague Trista Morrison makes that case cogently here.

Put simply, Qnexa has twice blown through the FDA's required "5 percent better than placebo" weight-loss standard. And if this press release is to be believed, there are no significant safety problems.

What could possibly go wrong? Three things:

1. History: The history of diet drugs is simple to understand. They either don't work, are dangerous, or are effective but so unpleasant that -- like GlaxoSmithKline's Alli -- few can stand to use them. So on the track record alone, if you think Qnexa is $10 billion-a-year drug, you're betting against history.
2. Qnexa is a speed-based antidepressant: This drug is literally a mixture of the amphetamine phentermine and the epilepsy/antidepressant drug topiramate (Topamax). And while Vivus's testing has not turned up any major side effect signals, the Qnexa proposition essentially asks doctors to prescribe the drug to patients who are neither depressed nor epileptic nor fatigued. Is it likely that widespread use of such a mixture will lead to zero worrying side-effect signals?
3. Qnexa is too effective: Remember, to succeed it is not good enough to simply be effective. Wyeth's infamous Fen-Phen was effective. Cocaine and cigarettes are effective. It's just that extended use of these products results in death. In Vivus's most recent test, patients lost up to 13.2 percent of their body weight. That's fine if you weigh more than 250 pounds, as the patients in the test did. But it's ruinously unhealthy if you weigh around 120 pounds or less. Thus, the FDA may ban it for patients who aren't fantastically heavy -- and that could restrict its revenues.

We'll see. $10 billion in sales are on the line, if the bulls are to be believed.

Image by Flickr user Qole Pejorian, CC.

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