A 32-year-old woman with moderate persistent asthma has been prescribed inhaled fluticasone propionate 250 μg twice daily for 6 months. She reports good symptom control with reduced exacerbations. On routine follow-up, you note she has developed oral candidiasis and mild hoarseness. Her serum cortisol at 8 AM is 18 μg/dL (normal: 10–20 μg/dL). Which of the following is the most appropriate next step in management?