Merck, the second-biggest U.S. drugmaker, on Wednesday said outside monitors recommended that its late-stage study of odanacatib, a new type of treatment, be stopped early because data has already shown it reduces fractures. Shares of Merck rose 4.2 percent on Thursday, on boosted hopes for the medicine.

Merck needs approvals of odanacatib and other medicines to help offset expected plunging sales of its flagship product, the $6 billion-a-year asthma treatment Singulair. Within months, Singulair will begin facing competition from cheaper generics in the United States.

Deutsche Bank analyst Barbara Ryan said odanacatib and four other drugs that Merck is expected to submit for regulatory approval by next year have "multibillion dollar sales potential."

"The market has not given the company credit for a pipeline," Ryan said. "Therefore this result is a definitive and psychological positive."

Leerink Swann analyst Seamus Fernandez, who had predicted peak annual sales of $975 million for odanacatib in 2020, said sales could reach $3 billion if final data from the study confirms it can safely reduce fracture risk by more than 40 percent.

Standard current treatments for osteoporosis, Merck's own Fosamax and Actonel from Warner Chilcott, belong to a family of medicines called bisphosphonates that can reduce bone fractures by 35 to 40 percent. But they have been associated with a range of side effects, including stomach and muscle pain, as well as relatively rare thigh bone fractures and jaw decay.

"Odanacatib's excellent tolerability profile would make it the drug of choice in the 20 to 30 percent of patients intolerant to bisphosphonates," Fernandez said in a research report.

Other medicines winding their way through late-stage trials at Merck have seen mixed results.

In February, hopes wilted for the most important of Merck's experimental medicines, a blood clot preventer called vorapaxar, when it was associated with excessive bleeding in one of the biggest heart trials ever conducted. Once heralded as a potential $3 billion-a-year drug, Wall Street has essentially written off the medicine.

Merck had acquired vorapaxar, which prevents blood clots through a new mechanism of action, in its 2009 purchase of rival drugmaker Schering-Plough, and it had been considered the crown jewel of Schering-Plough's own pipeline.

Confidence in Merck perked up a bit in June, when the company said its experimental insomnia drug suvorexant maintained effectiveness for 12 months in a late-stage study. It was the first sleep aid ever tested for a full year, and Merck reaffirmed it plans this year to seek marketing approval for the medicine.

Merck also plans this year to seek approval for Bridion, a medicine to reverse the effects of anesthesia that has been held up for several years by regulatory concerns. Bridion also came from Schering-Plough.

Next year, it plans to seek approval for Tredaptive, a drug to boost "good" HDL cholesterol that has also faced long regulatory delays because of safety concerns.

In clinical trials, Tredaptive raised HDL levels by 20 percent, while cutting "bad" LDL cholesterol by 18 percent.

(Editing by Leslie Adler)

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