A 52-year-old man with known cirrhosis (Child-Pugh C) presents to the emergency department with haematemesis and melaena. On examination, he is hypotensive (BP 85/55 mmHg), tachycardic (HR 118/min), and has clinical signs of ascites. Endoscopy reveals actively bleeding oesophageal varices. After initial resuscitation and variceal ligation, he is started on a vasoconstrictor. Which of the following is the most appropriate vasoconstrictor choice for this patient?