Aug 22 (Reuters) - Liquidia ( LQDA ) has filed a legal

challenge to the U.S. Food and Drug Administration's decision to

grant a three-year exclusivity to United Therapeutics' ( UTHR )

inhaled drug used to treat lung disorders, the drugmaker said on

Thursday.

The FDA on Monday delayed a traditional approval for

Liquidia's ( LQDA ) Yutrepia, which means that the company can only

launch the drug once patents on United's Tyvaso DPI expire in

May 2025.

Tyvaso DPI and Yutrepia are inhaled drugs used to treat

pulmonary arterial hypertension (PAH) and pulmonary hypertension

associated with interstitial lung disease (PH-ILD).

Liquidia ( LQDA ) filed the litigation in the district court of the

District of Columbia.

The company has faced multiple setbacks to bringing Yutrepia

to the U.S. market. The drug was granted tentative approval in

2021 to treat PAH, but Liquidia ( LQDA ) could not market it due to a

regulatory stay related to a patent infringement dispute with

United.

The FDA on Monday only allowed tentative clearances for

Yutrepia for both PAH and PH-ILD.

United has also sued Liquidia ( LQDA ) for patent infringement of its

drug Tyvaso.

In February, United filed a case with the FDA in alleging

that due procedure was not followed in allowing rival Liquidia's ( LQDA )

application to market Yutrepia to also treat PH-ILD, although it

voluntarily dismissed the complaint earlier this month.

Shares of Liquidia ( LQDA ) were down 2.7% at $9.71 in premarket

trading.

(Reporting by Sneha S K; Editing by Mrigank Dhaniwala and Varun

H K)