Macitentan 
Macitentan, also called ACT-064992, is a novel, highly potent, tissue-targeting dual ET-1 receptor antagonist characterized by a high lipophilicity [247]. Macitentan has been tested in the largest, long-term, event-driven randomized, controlled study (SERAPHIN, Study with an Endothelin Receptor Antagonist in Pulmonary arterial Hypertension to Improve clinical outcome) [246]. The Seraphin study was designed to evaluate the efficacy and safety of macitentan through the primary endpoint of time to first morbidity and all-cause mortality event in 742 patients with symptomatic PAH. Patients were treated for up to three and a half years.
Macitentan has met its primary endpoint, decreasing the risk of a morbidity/mortality event over the treatment period versus placebo. Secondary efficacy endpoints, including change from baseline to month six in 6-MWD, change from baseline to month six in NYHA FC and time – over the whole treatment period - to either death due to PAH or hospitalization due to PAH, also showed a dose-dependent effect. Treatment with macitentan in this study was well tolerated; headache, nausea and vomiting were reported as minor adverse events [248]. The safety set comprised 741 patients, who received at least one dose of study treatment (placebo, 3 mg or 10 mg). The number of adverse events reported and patients discontinuing treatment due to adverse events was similar across all groups. Similar elevations of liver aminotransferases greater than three times the upper limit of normal were observed in all groups. In addition, no difference was observed between macitentan and placebo in terms of fluid retention (edema). A decrease in hemoglobin - reported as an adverse event - was observed more frequently on macitentan than placebo, with no difference in treatment discontinuation between groups.