An 80-year-old man with dementia and congestive heart failure is admitted to hospital with delirium secondary to a urinary tract infection. He becomes very agitated and aggressive, posing a risk to himself and staff. Non-pharmacological methods (reassurance, reorientation, environmental modification) have been attempted but are ineffective. According to NICE guidelines on delirium, if pharmacological sedation is deemed necessary, what is the recommended first-line oral medication for short-term use?