Intervention: Hydroxyurea
Trial phase: Phase 2
ATC code: L01XX05
SMILES: NC(=O)NO
Sex: All
Age groups: Child | Adult
Healthy volunteers: No
Participants at risk: 1
Group description: In Arm 1 of this study, n=18 infants ages 9 months to 2 years will be administered an extemporaneous oral liquid formulation of HU on a single occasion followed by PK sampling. The dose administered will be ~20 mg/kg/day or the infant's usual daily dose.

Hydroxyurea: Drug: Hydroxyurea oral liquid dose administered will be 20mg/kg/day or infants's usual daily dose.
Eligibility criteria:
Inclusion Criteria:

Participants will be eligible for this study if only if all of the following inclusion criteria apply:

Laboratory (i.e. electrophoretic, chromatographic or DNA) confirmation of HbSS or HbSβ0thalassemia.
Participants may or may not be currently receiving HU. If participants are taking HU, then their most recent dose must be ≥24 hours prior to the start of the study.
Participant is in the "well" state (defined by ≥ 2 weeks since the last SCD-related complication).
Clinical evidence of normal gastrointestinal function and structure.
No clinical evidence of hepatic compromise, including transaminases < 3 times the upper limit of normal.
Estimated glomerular filtration rate (Schwartz equation) > 70 ml/min/1.73m2.
Body mass index (BMI) ≥5th and ≤95th percentile as per CDC growth charts.

In addition:

For the Pharmacokinetic Study (Arm 1):

Age ≥ 9 months and < 2 years.
Able to consume a minimum of 30 ml of water following ingestion of the study article.

For the Bioavailability Study (Arm 2):

Age ≥ 2 years and ≤ 18 years.
Weight of ≥ 10 kg
Females of child-bearing potential must have a negative pregnancy test prior to dosing and be willing to practice appropriate contraceptive measures, including abstinence, from the time of the initial pregnancy testing through the remainder of the study (30 days after last administration of investigational agents).
Males of child-bearing potential must be willing to practice appropriate contraceptive measures, including abstinence, during study participation (30 days after last administration of investigational agents).
Able to ingest both sprinkles and capsule study articles and consume a minimum of 30 ml of water following ingestion of each agent.

Exclusion Criteria:

Chronic transfusion therapy, or transfused within 3 months of study participation.
Known renal impairment (creatinine >1.5x the upper limit of normal for age).
Known hepatic impairment or Grade 2 or higher transaminases and bilirubin levels.
Diagnoses other than sickle cell anemia or sickle beta-zero thalassemia (i.e., other sickle cell variants or sickle/ hereditary persistence of fetal hemoglobin).
Blood count parameters as follows: hemoglobin <6.0 gm/dL, absolute reticulocyte count <80,000/mm3, absolute neutrophil count <1000/mm3, or platelet count <80,000/mm3.
The participant has used opiates, H2 blockers, proton pump inhibitors, antacids, other GI motility agents or any other medication that, in the opinion of the investigator, will interfere with the study procedures or affect the interpretation of the results of the study for 3 days prior to the first dose of study.
Participants taking antiretroviral drugs (including didanosine and stavudine) due to increased risk of toxicity with concomitant use.
Participation in another clinical intervention trial utilizing an IND/IDE agent, but can participate in HUGKISS since same drug agent.