Leukotriene Antagonists

A 34-year-old man from Mumbai with mild persistent asthma and seasonal rhinitis is prescribed montelukast 10 mg once daily at bedtime. After 3 weeks of therapy, he reports improved daytime symptoms and reduced nighttime awakening. However, his wife reports a marked change in his behavior—increased irritability, mood swings, and vivid nightmares. He denies suicidal ideation but admits feeling 'emotionally unstable.' What is the most appropriate next step in management?

A 28-year-old woman from Delhi presents with a 6-month history of persistent cough, wheezing, and dyspnea on exertion. She reports that her symptoms worsen with aspirin use and NSAIDs. Pulmonary function tests show FEV₁ of 68% predicted with a positive bronchodilator response. She is currently on inhaled salbutamol as needed but remains symptomatic. Her chest X-ray is normal. She is started on a leukotriene receptor antagonist. Which of the following is the PRIMARY mechanism by which this drug class provides bronchodilation in her case?