Macitentan is an orally active, dual endothelin receptor antagonist with tissue targeting properties. Macitentan inhibits both ETA and ETB receptors and prevents them from binding to ET-1. Macitentan displays high affinity and sustained occupancy of the ET receptors in human pulmonary arterial smooth muscle cells. One of the metabolites of macitentan is also pharmacologically active at the ET receptors and is estimated to be about 20% as potent as the parent drug in vitro. Macitentan is approved in the EU (as monotherapy or combination therapy) for the long-term treatment of pulmonary arterial hypertension (PAH) in adults of WHO functional class II or III, and in the USA for the treatment of PAH (WHO group I) to delay disease progression and reduce hospitalization for PAH.

ACT-132577 is the major and pharmacologically active metabolite of macitentan (ACT-064992), which is dual ETA/ETB endothelin (ET) receptor antagonist designed for tissue targeting.