MannKind Corporation (NASDAQ: MNKD) announced it is developing a dry powder inhalation formulation of ralinepag in collaboration with United Therapeutics Corporation (NASDAQ: UTHR) for treating pulmonary hypertension and fibrotic lung diseases.

United Therapeutics made an additional $5 million payment to MannKind in April to support the development of ralinepag DPI, designated as MNKD-1501. The collaboration operates under an existing agreement where United Therapeutics leads development, regulatory, and commercialization activities while MannKind handles formulation and supply.

MannKind is eligible to receive up to $35 million in development milestone payments and 10% royalties on net sales of any resulting commercial product. United Therapeutics plans to serve as the primary manufacturer of ralinepag DPI.

Ralinepag is an investigational prostacyclin receptor agonist with a long half-life and high potency in pulmonary vasculature. In March, United Therapeutics reported that its phase 3 ADVANCE OUTCOMES study of ralinepag extended-release tablets in pulmonary arterial hypertension met its primary endpoint with statistical significance.

The companies are currently formulating ralinepag DPI for planned non-clinical studies and a subsequent phase 1 study in healthy volunteers to assess dosing and pharmacokinetic comparability with oral ralinepag tablets. United Therapeutics initially intends to seek approval for pulmonary arterial hypertension, with plans to develop the product for additional conditions including pulmonary hypertension associated with interstitial lung disease, idiopathic pulmonary fibrosis, and progressive pulmonary fibrosis.

The collaboration builds on the companies' previous success with Tyvaso DPI, which received FDA approval in May 2022. United Therapeutics reported that Tyvaso DPI generated $1.3 billion in revenue in 2025.