NEW YORK (AP) -- Nektar Therapeutics' shares fell Monday on concerns that the recently approved diabetes drug Exubera wouldn't meet high commercial expectations.
Stock of the San Carlos, Calif.-based company slipped 86 cents, or 4.1 percent, to close at $19.89 on the Nasdaq Stock Market.
Nektar develops systems that deliver drugs by inhalation deep into the lung to treat systemic and respiratory diseases.
Exubera is a powdered form of insulin that can be inhaled. It is used for the treatment of patients with Type 1 and 2 diabetes and is an alternative to the widely used injectable form.
Nektar developed the delivery device for Exubera, and is partnered with Pfizer Inc.
"With the regulatory milestones now positively cleared, investors' attention will eventually shift to commercial prospects, which have the potential to disappoint overly bullish forecasts that drive (Nektar's) valuation," said Morgan Stanley analyst Jami Rubin, who downgraded the stock to "underweight" from "equal weight."
Still, other analysts, such as Lehman Brothers' Richard Silver, remained bullish on the stock.
"With Exubera's commercial potential still questioned by some, we see attractive risk/reward in the stock at current levels, particularly for investors with a longer-term time horizon," Silver said, maintaining his "overweight" rating.