GlaxoSmithKline (NYSE: GSK) says positive results from four late-stage studies of its experimental treatment for respiratory disease will support regulatory filings ahead of schedule.

Submissions for marketing approval will begin the end of this year after three additional studies of the LAMA/LABA treatment are completed, London-based Glaxo said in a statement Monday. The company is developing the drugs with Theravance Inc. of South San Francisco, California.

Glaxo and Theravance began a collaboration a decade ago to develop respiratory drugs to help succeed Advair, Glaxo’s aging best-seller.

“We are very encouraged by the results of these initial studies for our LAMA/LABA, an important cornerstone of our broad respiratory development portfolio,” said Darrell Baker, the Respiratory Portfolio Optimisation Leader at GSK, in the statement.

“These studies, together with our earlier dose-ranging work, give us confidence that this is a once-daily medicine with the potential to benefit many patients with COPD [chronic obstructive pulmonary disease],” he added. “Subject to successful completion of the ongoing studies, we plan to commence global regulatory filings from the end of this year.”

If successful, the LAMA/LABA treatment could replace more than half of Advair’s $7.8 billion in annual sales, according to analysts at UBS AG.

“LAMA/LABA data now suggest the sustainability of GSK’s respiratory franchise,” UBS analyst Gbola Amusa said in a note to investors today.

“There remains a great unmet medical need in COPD. In particular, physicians have stated that there is still a need to help patients breathe better,” said Rick Winningham, chief executive officer of Theravance. “There remains a great unmet medical need in COPD. In particular, physicians have stated that there is still a need to help patients breathe better. We believe the results of these initial studies demonstrate a potential benefit for patients with COPD.”

Full results from the studies may be presented at the European Respiratory Society’s annual meeting in Vienna starting Sept. 1, Amusa said. The product would compete with Spiriva from Boehringer Ingelheim GmbH and Pfizer Inc. and an experimental treatment being developed by Novartis AG.

LAMA/LABA may generate 1.7 billion pounds in sales, or 5 percent of total revenue, by 2021 and 20 percent of revenue growth over the next 10 years, Barclays Plc analysts said in a note today.

The once-daily treatment combines a long-acting muscarinic antagonist, which helps dry secretions in the respiratory tract, and a long-acting beta2 agonist, which relaxes the muscle that can contract airways. The drugs primarily treat respiratory disease caused by smoking.

Glaxo in April agreed to pay $212.9 million to boost its stake in Theravance to 26.8 percent. The companies also jointly developed Relovair, which Glaxo plans to submit for regulatory approval for chronic obstructive pulmonary disease in the U.S. and Europe and for asthma in Europe later this year.

GSK operates its North American headquarters in Research Triangle Park.

(Bloomberg news contributed to this report.)