A 3-year-old boy from rural Maharashtra presents with recurrent episodes of vomiting, lethargy, and hypoglycemia triggered by fasting or intercurrent illness. Serum lactate is markedly elevated (8 mmol/L; normal <2), and urine organic acids show elevated methylmalonic acid. Genetic testing confirms methylmalonyl-CoA mutase deficiency. The child is currently stable on oral intake. What is the most appropriate immediate next step in management?