Editor's note: This is a special reprint of the May 29, 2012, issue of BioWorld Insight.

Following Arena Pharmaceuticals Inc.'s big win for obesity drug Belviq (lorcaserin), Vivus Inc.'s Qnexa (phentermine/topiramate) is next in line. And, with a positive recommendation from the Endocrinologic and Metabolic Drugs Advisory Committee (EMDAC) that drug also looks like it will get past the FDA on its second attempt. (See BioWorld Today, Feb. 23, 2012, and May 11, 2012. Also see story this issue.)

But rather than a Clash of the Titans epic battle for market share, analysts expect the two obesity drugs to coexist. The competition is "more a construct of Wall Street," Rodman & Renshaw analyst Michael King told BioWorld Insight.

The market is large enough for both drugs, considering that 78 million U.S. adults are obese, and very few are taking Xenical (orlistat, Roche AG), the only prescription drug approved to treat the disease. "I don't see the two drugs cannibalizing each other for some time to come," King said.

Qnexa's new PDUFA date is July 17 after the FDA told the company it needed more time to review the recently submitted proposed REMS.

Meanwhile, Arena's launch is expected to be delayed. But either way, a headstart isn't expected to be much of a long-term advantage since patients are likely to switch between the two drugs. "This is about fitting the right drug to the right patients," King said.

In fact, Simos Simeonidis, analyst with Cowen & Co., said that launching together could be beneficial. "This is a market that has to be educated about these drugs and the space. They'll be symbiotic in some sense because they want to make a bigger market," he told BioWorld Insight.

While many patients likely will try both drugs over their lifetimes, the drug that can grab patients first is likely to register higher sales since those patients who respond to a drug will probably stick with it.

The REMS could be a potential stumbling block for Qnexa, which is expected to have a program to avoid its use in pregnant patients. "It can potentially be an impediment because you have to check extra boxes," Simeonidis said. But he pointed out that if lorcaserin also gets a REMS, "it's a wash," and might not be that big of deal anyway since doctors will want to use the best drug for their patients even if it means jumping through extra hoops. (Editor's note: Arena's drug was approved without a REMS, but the firm is required to do six postmarketing studies.)

King concurred that a REMS isn't as much of an impediment: "The need is so great. I don't think that'll hold things back."

Since primary care physicians and perhaps even gynecologists will prescribe the drugs, given the large percentage of women in the clinical trials, the key opinion leaders (KOLs) could play a vital role in the prescription habits.

King said the KOLs will have the greatest impact on ensuring that the drugs go to the right patients given the side effects. That could favor Qnexa over lorcaserin since Qnexa's major side effect, potential birth defects, is easier to stratify than lorcaserin's perceived risks, tumors in animal models and valvulopathy.

The one area where lorcaserin has a clear advantage is in marketing muscle. Arena has partnered with Eisai Inc., while Qnexa remains currently unpartnered. Given the large size of the market and the need for education, that could be a large advantage if Vivus launches alone.

No obesity drug has reached blockbuster status yet, but analysts think Qnexa and lorcaserin have a chance. "The difference is these drugs are actually efficacious. The older drugs were unsafe or didn't work," King said.

Piper Jaffray analyst Edward Tenthoff forecasts U.S. sales of lorcaserin to reach $1.9 billion in 2018.

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