UPDATE 1-U.S. FDA declines to approve United-Mannkind's lung disease therapy

(Adds background, Mannkind shares)

Oct 18 (Reuters) - The U.S. Food and Drug Administration has declined to approve a lung disease therapy developed by United Therapeutics and Mannkind Corp, citing an inspection issue at a third-party facility.

United said on Monday the health regulator's draft label for the drug, Tyvaso DPI, includes its use as a treatment for pulmonary arterial hypertension (PAH), as well as PAH associated with interstitial lung disease (PH-ILD).

In its complete response letter, the agency did not cite any deficiencies related to operations at MannKind's device manufacturing and testing facility for Tyvaso DPI.

Shares of Mannkind were down 17.9% at $4.18 in premarket trading.

While PAH is a type of high blood pressure that affects blood vessels in the lungs, PH-ILDs are a group of diseases that cause inflammation and scarring of the lung tissue, making it harder to breathe. (Reporting by Manas Mishra and Bhanvi Satija in Bengaluru; Editing by Ramakrishnan M.)