A Study of Intravenous L-Citrulline in Patients Aged 6-21 Years Old With Sickle Cell Disease Presenting to Emergency Departments in Acute Vaso-Occlusive Crisis

This study is being done to learn more about a possible new treatment for pain episodes (called vaso-occlusive crises or VOCs) in children, teens, and young adults with sickle cell disease (SCD). The study will include about 120 participants between the ages of 6 and 21 who come to the emergency department (ED) with a VOC. A VOC is a painful episode that happens with no clear cause and no signs of infection or major problems with organs like the liver or kidneys. Before joining the study, patients and their families may be asked to learn about it and give permission (called consent or assent) while at a regular clinic visit. If that hasn't happened yet, the consent/assent process will happen at the emergency department when the patient comes in for care. If the patient meets all the study requirements, they can join the treatment part of the study. Participants will be randomly assigned (like flipping a coin) to receive either: L-citrulline, the study drug, or A placebo, which looks the same but has no active ingredients. Everyone has an equal chance of getting either one. The study drug is given through an IV. It starts with one larger dose, followed by a steady infusion for up to 12 hours. All patients in the study will still receive the usual pain treatment (called standard of care), which may include opioids. However, some patients may need fewer opioids if the study treatment helps with their pain. If any medicines are not allowed during the study, the doctor will explain this during the consent process. Patients can go home once: Their pain is controlled with oral (by mouth) pain medicine, They're eating and drinking well, and They've been given a personal pain management plan to use at home. After leaving the hospital, the study team will follow up with patients by phone about 2 days later (within a 12-hour window), again around Day 7, and again around Day 30 to check how they're doing.