GlaxoSmithKline's (NYSE: GSK) inhaled drug candidate Relovair is showing positive results in two crucial studies evaluating the compound as a treatment for chronic obstructive pulmonary disease, or COPD.

The results boost the compound's prospects as a successor to GSK's blockbuster asthma and COPD drug Advair, whose patents have expired. London-based GSK, which maintains its U.S. headquarters in Research Triangle Park, North Carolina, and drug partner Theravance (Nasdaq: THRX) on Thursday released the results of two efficacy and safety phase 3 studies of Relovair that evaluated the compound in patients with COPD. GSK said both studies, which evaluated the compound in 6,000 patients, showed that Relovair demonstrated statistically significant improvement in patients compared to a placebo.

The two six-month studies will be combined with a separate 12-month study and included in the company's regulatory submissions. The company said that full results of all studies will be presented at future scientific meetings.

Relovair, which has been developed as a once-per-day inhaled drug, is also being studied as an asthma treatment. The drug candidate is a combination treatment that pairs Advair's main ingredient fluticasone with another compound, vilanterol. Advair, which generated about $8.4 billion in 2010 sales, is GSK's top-selling product.

GSK entered a strategic alliance with San Francisco, California-based Theravance in 2004 that gave GSK exclusive access to the biopharmaceutical company's drug discovery programs prior to Sept. 1, 2007. The alliance includes Theravance's drug program for COPD. Under the agreement, GSK is responsible for funding all development, manufacturing, and commercialization of the compounds.