A 67-year-old man with type 2 diabetes, CKD stage 3 and hypertension presents with a 1-week history of black tarry stools and dizziness. He takes aspirin and an ACE inhibitor. On examination, he is pale, blood pressure 90/60 mmHg, heart rate 110 bpm. Abdominal examination is soft, but PR reveals melaena. What is the most appropriate immediate management?