A 6-year-old boy is brought to the emergency department by his mother with a 2-hour history of acute dyspnea and wheezing. He was playing outside during high pollen season when symptoms began abruptly. His past medical history is significant for intermittent asthma managed with albuterol as needed. On physical examination, the patient appears anxious, has bilateral decreased air entry with prolonged expiratory phases, and speaks only in short phrases. Vital signs are: heart rate 120 bpm, respiratory rate 32/min, blood pressure 105/68 mmHg, and oxygen saturation 88% on room air. Peak expiratory flow is 45% of predicted for his age. Which of the following is the most appropriate initial management?

1. A)Supplemental oxygen alone followed by reassessment in 1 hour
2. B)Nebulized albuterol, ipratropium bromide, and systemic corticosteroids with supplemental oxygenGABARITO
3. C)Chest radiograph and empiric antibiotics to rule out bacterial infection
4. D)Oral prednisone and discharge home with urgent outpatient follow-up in 24 hours
5. E)Intravenous magnesium sulfate as single-agent therapy while awaiting response to observation