GlaxoSmithKline said on Monday it planned to file its key new lung drug Relovair for regulatory approval in mid-2012, following the release of a batch of generally encouraging clinical trials results.

Although the new once-a-day inhaled treatment did not show superiority to GSK's existing twice-daily drug Advair, Britain's biggest drugmaker said the totality of the data gave it confidence about the medicine's prospects.

The convenience of Relovair's once-daily dosing ix expected to give it an importance edge in the multibillion-dollar market for lung medicines.

Relovair, which is being developed with U.S.-based Theravance , will be filed for chronic obstructive pulmonary disease (COPD) in the United States and Europe in the middle of the year.

It will also be submitted as a new treatment for asthma in Europe at the same time, while in the United States GSK will continue discussions with regulators on its use in asthma.

(Reporting by Ben Hirschler)