Diet pill maker Vivus (VVUS) saw demand rise substantially for its weight-loss drug Qsymia in the second week on the market. Some insurers appear to be covering the product.

The sales figures were a cause for celebration among investors, at least for a short spell. Shares of Vivus rose 10% Monday to close at $20.44. The stock rose another 2% Tuesday morning, but pared gains by early afternoon, trading around $20.50.

With the hype around recently approved diet drugs from Vivus and rival Arena Pharmaceuticals (ARNA), sales figures will certainly be a significant guidepost for investors.

Both stocks enjoyed big rallies this year. Vivus shares more than doubled, while Arena jumped 370%. Arena's drug, Belviq, is approved by the U.S. Food and Drug Administration but is still being reviewed by the U.S. Drug Enforcement Administration because of potential for abuse. The pill is expected to be on the market by late this year or early 2013. Arena's development partner, Japanese drugmaker Eisai, will sell Belviq.

Two drug-tracking companies, IMS Health and Wolters Kluwer, reported substantial gains for Qsymia in the second week of sales, which ended Sept. 28. The numbers vary quite a bit and it should be noted that these are quite early figures.

According to Cowen & Co. analyst Simos Simeonidis, IMS reports 933 new prescriptions compared with 236 the first week, and Wolters Kluwer said there were 581 new prescriptions vs. 106 the first week.

"Even though we believe it is too early in the launch to call anything a trend, we see the four- and five-fold increase in the IMS and Wolters Kluwer numbers as a positive early sign for Qsymia’s demand," Simeonidis says.

So why does the analyst have a hold rating on the stock?

Simeonidis says he believes that Qsymia will be a big-selling drug -- $1.6 billion by 2019. But he also says the ramp-up will be slower than some investors think. Vivus and Arena just won approvals for the first new diet pills in the U.S. in 13 years. Both companies are appealing to doctors' concerns that obesity has become an epidemic, leading to a host of related diseases. The long stretch of time between the new drugs and past approvals is a reflection of the safety concerns associated with these type of products.  

"The Qsymia launch will be a slow one, given that the company will have to build out awareness for both the disease and the drug," Simeonidis says.

Vivus is trying to create demand for a drug with physician obesity specialists through a 150-person sales force, which is a challenge, Simeonidis says. He predicts shares will "remain range bound" for the next nine to 12 months.

Meanwhile, Bloomberg reported earlier this month that 30% of health insurers were covering the pill. Qsymia is only distributed through mail order pharmacies and the major players in that business, including Express Scripts (ESRX), Walgreen (WAG) and CVS Caremark (CVS), have all lined up to sell the drug, Vivus says. It costs about $4 to $6 a pill, depending on the dosage.

Orexigen Therapeutics (OREX) also is testing a diet pill that it hopes to eventually bring to market to compete with Vivus and Arena's drugs.

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