A 3-year-old boy from rural Maharashtra presents with progressive weakness, developmental delay, and recurrent infections. Serum lactate is 8 mmol/L (normal <2), and pyruvate is elevated. Muscle biopsy shows ragged-red fibres. Genetic testing confirms a mutation in MT-CO1 (mitochondrial cytochrome c oxidase subunit 1). What is the most appropriate immediate next step in management?