A 28-year-old woman from Delhi presents with a 6-month history of progressive muscle weakness, myalgia, and dark urine after exercise. Laboratory investigations show elevated serum creatine kinase (CK: 8000 U/L), myoglobinuria, and a serum glucose of 48 mg/dL during a symptomatic episode of muscle pain and weakness. Muscle biopsy shows absent phosphofructokinase (PFK) activity. Which is the most appropriate immediate next step in management?