• Contraindication in patients with severe hepatic impairment (with or without cirrhosis) and in patients with baseline values of hepatic aminotransferases (AST and/ or ALT) > 3X ULN. • Hepatic aminotransferases (ALT and/ or AST) should be evaluated prior to initiation of ambrisentan. • During therapy, monthly monitoring of ALT and AST is recommended. • Discontinuation of ambrisentan therapy if patients develop sustained, unexplained clinically significant ALT and/ or AST elevation or if ALT and/ or AST elevation is accompanied by signs or symptoms of hepatic injury (e. g. jaundice). • In subjects without clinical symptoms of hepatic injury or jaundice, reinitiation of ambrisentan may be considered following resolution of hepatic enzyme abnormalities.