Ambrisentan, an endothelin receptor type A-selective endothelin receptor antagonist, for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a disease of the pulmonary vasculature characterized by vasoconstriction and vascular proliferation, which leads to right heart failure and death. Prostacyclin, NO and endothelin are felt to be key mediators in the development of PAH. We present the available published and presented data about ambrisentan, an ET(A)-selective endothelin receptor antagonist (ERA) and newest ERA agent to be approved by the FDA for the treatment of PAH in patients with WHO functional class II and III symptoms. Randomized, placebo-controlled trials have demonstrated a significant improvement in exercise capacity and decrease in time to clinical worsening, along with evidence to support an improvement in WHO functional class and quality of life for patients receiving ambrisentan. Long-term data have shown a 1-year survival of 95%; of the survivors, 94% remained on ambrisentan monotherapy. Endothelin receptor antagonists as a drug class have previously been associated with peripheral edema, aminotransferases abnormalities and a teratogenic risk to a developing fetus. Peripheral edema was observed in patients receiving ambrisentan; however, a greater percentage was experienced in patients aged > 65 years. In contrast, significant aminotransferase abnormalities were not observed with ambrisentan treatment in the placebo-controlled trials, and in all clinical trials combined the 1-year risk seems to be low (< 3%). Despite these data, the FDA requires monthly liver function tests monitoring. As with other ERAs, monthly pregnancy testing is required in all women of child bearing potential.