A 6-year-old boy presents with acute asthma exacerbation. Vitals: HR 128/min, RR 32/min, BP 105/68 mmHg, SpO₂ 89% on supplemental oxygen, temperature 37.2°C. He receives continuous nebulized albuterol and IV methylprednisolone. After 2 hours, peak expiratory flow remains 50% of predicted with persistent diffuse wheezing. Chest X-ray shows hyperinflation without pneumothorax. He denies chest pain. Which intervention is most appropriate?

1. A)Add IV magnesium sulfateGABARITO
2. B)Discontinue corticosteroids to avoid immunosuppression
3. C)Switch to ipratropium bromide as monotherapy
4. D)Administer systemic antibiotics for presumed infection
5. E)Intubate immediately without further medication trials