Clinical Study to Compare the Efficacy and Safety of Macitentan and Tadalafil Monotherapies With the Corresponding Fixed-dose Combination Therapy in Subjects With Pulmonary Arterial Hypertension (PAH)

PAH is characterized by a progressive increase in pulmonary arterial pressure (PAP) and in pulmonary vascular resistance (PVR) potentially leading to right heart failure and death. Current PAH-specific therapeutic options include treatments that target the three pathways (endothelin, nitric oxide, and prostacyclin pathways). While combination treatment is common, FDC pills or tablets that combine two or more PAH-specific therapies are not available, thereby requiring participants to take multiple pills/tablets daily. An FDC is an attractive option for PAH participants because it simplifies the treatment regimen by combining two therapies (which would otherwise involve a total of three tablets: one macitentan 10 mg tablet and two tadalafil 20 mg tablets) into a single tablet. Macitentan is an orally active, non-peptide, potent dual endothelin receptor A and B antagonist. Tadalafil is a selective inhibitor of phosphodiesterase type-5 (PDE-5), the enzyme responsible for the degradation of cyclic guanosine monophosphate (cGMP). This study comprises the following consecutive periods: Screening period (lasts up to 30 days), Double-blind treatment period (consists of the titration phase \[the first 2 weeks\] and the maintenance phase \[Week 3 through Week 16\]), Open-label treatment period, End-of-Treatment (EOT), Safety follow-up (S-FU) period, and End of Study (EOS). The total study duration for a participant will be up to 30 months. Study assessments like physical examinations, vital signs, right heart catheterization, 6-minute walk test will be performed. Safety will be assessed throughout the study.