A 58-year-old man with a 20-year history of alcohol use disorder presents to the emergency department with haematemesis and melaena. On examination, he has spider angiomas, ascites, and a palpable spleen. Upper endoscopy confirms oesophageal varices with active bleeding. After initial resuscitation and variceal ligation, what is the most appropriate next step in management to prevent variceal rebleeding?