A 60-year-old woman is on ICU day 8 following a major abdominal operation complicated by septic shock. She is now extubated and haemodynamically stable. She is agitated, unable to maintain attention, and has vivid visual hallucinations. RASS fluctuates between +1 and -2 during the day. CAM-ICU is positive. Which pharmacological intervention has the best evidence for treating hyperactive ICU delirium?