When you're

a small public company, you usually don't want to be one of the day's most actively traded stocks.

Invariably, it means bad news has unnerved investors.

So it was Tuesday with NuPathe Inc., a 61/2-year-old Conshohocken drug-development firm, when it disclosed that federal regulators had questions that will delay the launch of its first product.

NuPathe said the Food and Drug Administration issued a complete-response letter in connection with its review of the migraine treatment Zelrix. The letter means that while regulators have completed their review of NuPathe's new-drug application, the FDA won't approve the product until certain questions are answered.

The FDA itself doesn't disclose the content of its complete-response letters. In a statement, NuPathe said the questions centered on chemistry, manufacturing, and safety issues. The company also said it either had "sufficient data" to answer them or would have that data soon.

NuPathe executives weren't available for comment Tuesday, and the company makes it a practice of not commenting on its discussions with the FDA. However, in a statement, NuPathe chief executive Jane H. Hollingsworth did say the letter "gives us confidence that we can provide the information needed to support FDA approval for our migraine patch in a timely manner."

However, investors appeared to be lacking in confidence. NuPathe shares, which had closed at $4.05 on Monday, lost 35 percent, or $1.40, to $2.65. In all, 5.76 million shares traded hands, or more than 58 times its average daily volume over the last 52 weeks. It was one of the most actively traded local stocks Tuesday.

Still, a regulatory delay doesn't mean the drug will never get approved. NuPathe's statement, which conveys its optimistic viewpoint, said the

letter meant it won't launch its Zelrix migraine patch in the first half of 2012, as it had previously announced.

In a note to investors, Wedbush Securities analyst Liana Moussatos said her firm was anticipating a six-month delay, meaning a September 2012 launch for Zelrix. The West Coast firm also estimates peak annual sales potential for the drug to be more than $300 million.

If Zelrix eventually does win FDA clearance, the drug will join a crowded market for the treatment of migraines, which affect about 31 million people in the United States. Merck & Co. Inc.'s Maxalt had U.S. sales of $496 million in 2010. GlaxoSmithKline P.L.C. sells Imitrex and Treximet. IMS Health Inc., which tracks prescription-drug sales, said U.S. sales of migraine drugs totaled more than $1.7 billion in 2010.

The regulatory delay also means that NuPathe will hold off on hiring about 100 sales representatives to call on headache specialists and neurologists. In a conference call with analysts Aug. 15, Hollingsworth said the company would not bring sales reps on board until about 30 days before the launch of Zelrix.

Still, the delay is a significant speed bump for one of the few local venture-backed companies to go public in the last three years.

Its initial public offering price last August? Ten dollars per share.

Contact columnist Mike Armstrong at 215-854-2980 or marmstrong@phillynews.com,
or @PhillyInc on Twitter.
Read his blog, "PhillyInc,"