Getting its first product, a painkiller, approved for sale was a triumph for BioDelivery Sciences.

Champagne corks popped at BDSI Thursday, the day the Food and Drug Administration let the small Raleigh drug development company know that Onsolis, a potent pain patch for cancer patients, had passed all regulatory hurdles. On Friday, analysts congratulated BDSI CEO Mark Sirgo during a conference call. By Monday, BDSI expected to have about $27 million more in the bank, a payment its Swedish partner Meda promised upon regulatory approval of Onsolis.

"It's been a long haul," Sirgo told analysts in the call Friday. "This is a fantastic day for our company."

So why did BDSI's stock drop 5 percent on a day when it should have risen?

Product sales are the holy grail for a research and development company that has lived off the good will of investors and partners for years. Revenue lowers the risk that the company will run out of money and indicates that profitability is within reach.

One analyst blamed BDSI's stock drop on the shareholder base, saying BDSI needs more long-term institutional investors. Another suggested that questions might have arisen about Onsolis' sales potential and investors bailed after their initial excitement wore off.

In fact, Onsolis will enter a market where three similar products generated about $700 million in annual sales last year. Two of the competitors are versions of Actiq, a fentanyl painkiller that went generic a few years ago. The third is Fentora, an Actiq successor that received regulatory approval in 2006. All three dissolve in the mouth and release fentanyl, a controlled substance.

BDSI's marketing partner Meda plans to start promoting Onsolis to oncologists, pain specialists and primary care doctors in the fall. The goal is to get about 100,000 patients on Onsolis within two years, Sirgo said. That's more than three times as many cancer patients as currently receive generic Actiq and Fentora combined for acute, breakthrough pain.

Sirgo acknowledged that's an aggressive goal, but he said Meda plans educational programs for physicians to convince them to switch patients to Onsolis and to prescribe Onsolis to cancer patients who have not received a fast-acting fentanyl painkiller. He declined to say how much Onsolis will cost.

Study results show that Onsolis delivers more fentanyl in a shorter time than Actiq, according to a presentation BDSI made at a March health care conference for institutional investors. No studies comparing Onsolis and Fentora have been done.

Also, Onsolis delivers fentanyl without taste distortions.

But Onsolis will come to market with more safety requirements, called Risk Evaluation and Mitigation Strategies, than Fentora now has. The FDA is requesting REMS for all opioid pain medications, including fentanyl, morphine and oxycodone, to make sure the drugs' benefits outweigh their risks, which include death from overdose.

An FDA decision on Fentora's REMS is due in October, but a delay would put Onsolis at a disadvantage and hurt sales, said Robert Hazlett, a pharmaceutical analyst with BMO Capital.

BDSI shares traded like hotcakes Thursday, going as high as $7.25 when the news on Onsolis' approval broke. Then they fell, to close at $6.15 Thursday. The drop continued on Friday, when shares lost 5 percent to close at $5.84.