a 45-year-old african-american man with no significant past medical history presents with a 1-hour history of left retroorbital headache. the headache was of a sudden onset and began upon waking that morning. it is described as excruciating, stabbing, sharp, and lancinating; it is rated as severe in intensity. he denies any preceding infections, nausea, vomiting, photophobia, or osmophobia; he also denies fever, chills, stiff neck, focal weakness, numbness, tingling, vision, hearing, gait, or speech changes. he recalls a similar episode several months ago; it lasted about a week, and it dissipated without complications. his physical exam is remarkable for painful distress, lacrimation with conjunctival injection, nasal congestion, rhinorrhea, left ocular miosis, and left forehead diaphoretic flushing. question: what pharmacologic agent is the most beneficial for this patient at this time?