Optimizing Hydroxyurea Dosage With Pharmakokinetic in Patients Suffering of Moderate to Severe Sickle Cell Anemia

The goal of this study is to evaluate if patients with sickle cell disease can achieve a maximum tolerate dose of hydroxuyrea (HU) over a period of 12 months faster with pharmacokinetic testing than the standard of care bloodwork follow-up. Pharmacokinetic test is used to evaluate the process by which drugs are absorbed, distributed in the body, localized in the tissues, and is excreted. Patient will be a randomized (coin toss method) into 2 groups. Group A will have an increase of their HU dosage with pharmacokinetic results and Group B will have an increase of their HU dosage following the standard of care bloodwork follow-up. Group C will include patient with sickle cell disease that has been taking HU for at least 12 months and will undergo a pharmacokinetic dosage to check the level of HU only one time.

Inclusion Criteria (Group A and B) : * Have had confirmed diagnosis of SCD at CHU Sainte-Justine biochemistry lab with hemoglobin electrophoresis. * Patients with SS, SBThal0. * Agree to take hydroxyurea for a period of 12 months * Be between age of 6months old and 18 years old. * Have consented for participation in the study. Inclusion Criteria (Group C) : * Have had confirmed diagnosis of SCD at CHU Sainte-Justine biochemistry lab with hemoglobin electrophoresis. * Patients with SS, SBThal0. * Have taken hydroxyurea for a period of at least 12 months, and have received HU at a stable dose and at MTD for at least 6 months. * Be between age of 6months old and 18 years old. * Have consented for participation in the study. Exclusion Criteria: * Patients with sickle cell genotype other than SS or SBThal0 (SC, SBThal+, SE or SD) * Patients on chronic transfusion program * Patients have received a blood transfusion in the last 4 weeks of study enrollment. * Have received a hematopoietic stem-cell transplantation * Creatinine \>2x normal for age * ALT\>2x normal for age * Sexually active females unwilling to comply with reliable method of birth control * Pregnancy * Conditions which in the opinion of the investigator, would compromise participation in the study will be excluded.