Adam is 47 years old and known to have cluster headaches. On this occasion the right sided temporal pain is excruciating and started 20 minutes ago prompting him to attend an urgent care centre. He is also feeling nauseous, although has not vomited and his right eye is watery. Past medical history includes well controlled Asthma requiring occasional salbutamol inhaler use. He has taken Paracetamol with no effect. Neurological examination is normal today and you explain he is experiencing a further acute cluster headache.
Which of these options would be least appropriate for his immediate management?