Safety and Efficacy of Ambrisentan in the Treatment of Pulmonary Arterial Hypertension

Three different classes of specific therapy exist for pulmonary arterial hypertension. Ambrisentan belongs to the endothelin receptor antagonist (ERA) class of drugs, which inhibit the action of Endothelin-1; a potent vasoconstrictor and mitogen. Unlike bosentan and sitaxentan, it has a propanoic-acid based structure and like sitaxentan it has selective affinity for type A Endothelin receptors. Two large randomized controlled trials (ARIES-1 and ARIES-2) have demonstrated clinical benefit with ambrisentan in pulmonary arterial hypertension by repeated measurement of 6-minute walk distance. The most common adverse effect associated with ambrisentan use is peripheral edema, the incidence of liver enzyme elevation seen is lower than for other ERAs. Ambrisentan is safe in combination with warfarin and sildenafil. It offers further flexibility in the treatment of PAH as monotherapy and in combination. Although encouraging, trial data do not exhibit improved efficacy compared with other ERAs or sildenafil and there are no direct comparison studies. Long-term outcome data, including subgroup analysis are awaited to see if there are particular benefits of this therapy in PAH.