The primary objective of this study is to evaluate the long-term safety of LIQ861 in patients with pulmonary arterial hypertension (PAH).

One of the greatest impediments to patient treatment satisfaction with current inhaled treprostinil therapy is inconvenience. Currently, PAH patients using inhaled treprostinil may require more than 36 breaths per day using a nebulizer requiring daily set up and cleaning. The use of a discrete, hand-held dry powder inhaler to deliver treprostinil to the lungs could represent a major improvement in convenience and patient satisfaction, thereby improving the quality of life for PAH patients. Liquidia is pursuing approval of LIQ861, an inhalation dry powder formulation of treprostinil that is produced using Liquidia's PRINT® Technology (Particle Replication in Nonwetting Templates), as an alternative to current inhaled treprostinil therapy for the treatment of patients with PAH (WHO Group 1).

Inclusion Criteria:

1. Evidence of a personally signed and dated informed consent document exists indicating that the patient has been informed of all pertinent aspects of the study prior to initiation of any study-related procedures.
2. Patient is willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures.
3. Patient has fulfilled all entry criteria at the time of enrollment in original study with LIQ861.
4. Patient has completed the protocol defined end of study procedures or met a protocol-defined and adjudicated endpoint in the original LIQ861 study in which they were enrolled.
5. Patient, whether male or female, agrees to use a medically acceptable method of contraception throughout the entire study period from informed consent through the termination visit, if the possibility of conception exists. Eligible male and female patients must also agree not to participate in a conception process (e.g., actively attempt to become pregnant or to impregnate, sperm donation, in vitro fertilization) during the study and for 30 days after the last dose of LIQ861.

Exclusion Criteria:

1. Patient prematurely discontinued LIQ861 due to a drug-related AE/SAE or tolerability issue in the original LIQ861 study in which they were enrolled, or patient did not complete protocol defined study procedures at an end of study visit (not Early Termination visit) in their original LIQ861 study.
2. Patient withdrew consent during participation in another LIQ861 study.
3. Patient is a female who wishes to become pregnant or who has a positive pregnancy test on Day 1 (LTI-302 Study Initiation Visit).
4. Patient has undergone lung or heart/lung transplant or the initiation of parenteral (intravenous [IV] infusion or subcutaneous injection) therapy with a prostacyclin during the time since participation in their original LIQ861 study.
5. Any reason exists that, in the opinion of the Investigator or Medical Monitor, precludes the patient from participating in the study, e.g., any previous or intercurrent medical condition that may increase the risk associated with study participation or that would confound study analysis or impair study participation or cooperation.