A Study of the Efficacy and Safety of MK-5475 in Participants With Pulmonary Arterial Hypertension (INSIGNIA-PAH: Phase 2/3 Study of an Inhaled sGC Stimulator in PAH) (MK-5475-007)

This is a two-part (Phase 2/Phase 3) study of MK-5475, an inhaled soluble guanylate cyclase stimulator, in participants with pulmonary arterial hypertension (PAH).

The first part (Phase 2) will assess three different doses of MK-5475 compared to placebo in a base period of 12 weeks, followed by comparison of three different doses of MK-5475 during an optional 40 month extension period. The treatment dose with the best efficacy and safety profile in the phase 2 cohort base period will be selected for use in the second part (Phase 3) of the study. The primary hypothesis of Phase 2 is that at least one MK-5475 dose is superior to placebo in reducing pulmonary vascular resistance (PVR) from baseline at week 12.

The purpose of the second part (Phase 3) of the study is to confirm the efficacy, safety, and tolerability of MK-5475 at the selected dose compared to placebo during a 12 week base period followed by an extension period of up to 5 years. The primary hypothesis of Phase 3 is that MK-5475 is superior to placebo in increasing 6-minute walk distance (6MWD) from baseline at week 12. Due to sponsor's decision this phase/part was not conducted.


Eligibility Criteria:
Inclusion Criteria:

* Pulmonary arterial hypertension (PAH) in one of the following groups:

  * Idiopathic PAH
  * Heritable PAH
  * Drug and toxin-induced PAH
  * PAH associated with connective tissue disease, HIV infection, or congenital heart disease.
* Diagnosis of PAH documented by right heart catheterization (RHC).
* Eligibility RHC meeting all of the following criteria:

  * Mean pulmonary artery pressure (mPAP) ≥25 mmHg
  * Pulmonary vascular resistance (PVR) of ≥3 Wood units
  * Pulmonary capillary wedge pressure (PCWP) or left ventricular end diastolic pressure (LVEDP) ≤15 mmHg.
* World Health Organization functional class (WHO-FC) symptoms between Class II and IV.
* Two 6-Minute walk distance (6MWD) measurements between 150 and 500 meters, one at screening and one at randomization.
* Stable concomitant background PAH-specific therapy.
* Body Mass Index (BMI) between 18.5 kg/m² and 40 kg/m² .
* Agree to be abstinent from heterosexual intercourse or use contraception during the intervention period and for at least 14 days after the last dose of study intervention.
* Female participants may not be pregnant or breastfeeding.

Exclusion Criteria:

* Group 2 to 5 pulmonary hypertension.
* PAH in one of the following groups:

  * Long term responders to calcium channel blockers
  * Overt features of venous/capillary involvement
* Evidence of more-than-mild obstructive lung disease.
* Evidence of more-than-mild parenchymal lung disease.
* Evidence of more-than-mild obstructive sleep apnea (OSA) that is untreated.
* Evidence or history of left heart disease, including any of the following:

  * Left ventricular ejection fraction (LVEF) ≤45%
  * Moderate or severe left-sided valvular disease (aortic or mitral valve stenosis or regurgitation)
  * Significant left ventricular diastolic dysfunction on echocardiographic evaluation
* Presence of 3 or more of the following risk factors for heart failure with preserved ejection fraction: BMI\>30 kg/m², essential systemic hypertension, diabetes mellitus of any type, or coronary artery disease.
* Oxygen saturation measured by pulse oximetry (SpO₂) \<90%, despite supplemental oxygen therapy.
* Chronic renal insufficiency (eGFR \<30 mL/min)
* Chronic liver disease (i.e., Child-Pugh B or C), portal hypertension, cirrhosis, or significant hepatic laboratory abnormalities.
* Current smoker or currently uses electronic cigarettes (vapes).
* History of cancer, except: nonmelanomatous skin carcinoma or carcinoma in situ of the cervix or other malignancies which have been successfully treated, with appropriate follow up, and unlikely to recur for the duration of the study.