Which asthma medication is most likely to cause agitation and nightmares in a patient?

Montelukast, commonly known by its brand name Singulair, is a leukotriene receptor antagonist used in the management of asthma and allergic rhinitis. This medication has been associated with neuropsychiatric side effects, including agitation, anxiety, and vivid nightmares. Clinical studies and case reports have noted these side effects in some patients, which has led to recommendations for monitoring mood changes in individuals taking the medication.

The other medications listed have distinct mechanisms of action and side effect profiles. Salbutamol (Albuterol) is a short-acting bronchodilator primarily affecting respiratory smooth muscle and is less likely to impact mood or cause agitation. Budesonide (Pulmicort), a corticosteroid, acts on inflammation but is not typically linked to neuropsychiatric effects, especially in the short-term usage common in asthma treatment. Ipratropium (Atrovent) is an anticholinergic that primarily focuses on bronchoconstriction without a known connection to mood disturbance or sleep issues.

Therefore, Montelukast's specific association with agitation and nightmares makes it the correct choice in this context.