Q: Name at least one most commonly used drug in ICU which causes diarrhea in its elixir form

Answer: Acetaminophen 

Acetaminophen elixir is preferred in ICU as it is easy to administer liquid form via feeding tube. But it is very hyperosmolar ( > 3,000 mosm/kg H2O) and may be a cause of diarrhea in ICU. Similar is the case with Potassium and multi-vitamin elixir.