A 65-year-old man with a history of NSAID use presents with melaena and postural dizziness. His heart rate is 110 bpm and BP 95/60 mmHg. He is resuscitated with IV fluids and blood tests are sent. Upper gastrointestinal bleeding due to peptic ulcer is suspected and urgent gastroscopy is being arranged. Which pharmacological therapy should be commenced as soon as possible?