Study design
Participants received a single intravenous infusion of phosphocreatine sodium according to their age (28 days ~ < 1 year old: 0.5 g, 1~ < 6 years old: 1 g, 6 ~ < 18 years old: 2 g). The above phosphocreatine sodium was dissolved in 50 ml 0.9% sodium chloride injection and continuously injected with an intravenous pump within 30 ± 2 min. Blood samples from the arm without an intravenous infusion were collected at baseline (before infusion) and, approximately 30, 40 or 50, 75 and 180 min after the start of infusion. The actual infusion time and sampling time were recorded. The blood samples were centrifuged at 4oC (3000 rpm) for 10 min, and the plasma at upper layer was separated and stored immediately at -40˚C until analysis.