Why Vivus's Qnexa Might Avoid the Obesity Drug Graveyard

(MoneyWatch)  Vivus's better-than-expected Phase III data with obesity drug Qnexa started the goldmine versus graveyard debate once again.

In one corner: the folks who think obesity is the last frontier of drug development, a vast promised-land that could generate annual sales topping $10 billion for any drug that conquers it.

In the other corner: the folks like BNET's own Jim Edwards, who argues that obesity "has been tapped on a regular basis for years and currently hosts several products, none of which are very successful" ?€" and that newcomers Vivus, Arena Pharmaceuticals and Orexigen Therapeutics face the same impending doom. (See the counter-post here.)

Both sides have a point, but Vivus's new data just might put Qnexa in position to overcome the hurdles that have stymied the field thus far.

The efficacy issue: The currently approved (and commercially unsuccessful) obesity drugs offer placebo-adjusted weight loss of 3 to 5 percent, while Qnexa delivered 9.4 percent in one of the recent studies. That's the difference between a 250-pound woman losing seven pounds or losing 23 pounds. Qnexa's efficacy edges toward that once offered by Wyeth's infamous Fen-Phen (dexfenfluramine/phentermine), which generated more than 20 million prescriptions annually ?€" proving folks will pay up if the drug works.

The safety issue: Qnexa combines super-low doses of two generic drugs that have a long history of use: the diet drug phentermine and the epilepsy drug topiramate. Yes, phentermine was the "phen" half of Fen-Phen, but it was the other half that proved deadly. And yes, phentermine raises blood pressure and is only indicated for short-term use. And yes, topiramate has some nasty side effects like cognitive problems and depression.

But so far in studies, Qnexa's low doses have checked out pretty clean. The most common side effects were dry mouth and tingling, and analyses looking for depression, suicidality, QT prolongation or cognitive/psychomotor impairment came up empty.

There's certainly still a risk that serious side effects could crop up once Qnexa is introduced in a broad population, but for now, Qnexa is looking less like another El Dorado and more like real gold.

Gold photo by Flickr user BullionVault, CC