Hydroxyurea Management in Kids: Intensive Versus Stable Dosage Strategies

This is a pilot study, single-blind, randomized, multicenter, therapeutic clinical trial designed to evaluate the feasibility of enrolling infants and toddlers (9 months to 36 months) with sickle cell anemia (SCA; HbSS or HbSβ\^0thalassemia), regardless of disease severity, to a therapeutic trial. A prior clinical trial at St. Jude Children's Research Hospital (SJCRH) (BABYHUG, NCT01783990) demonstrated that a fixed dose (20 mg/kg/day) of hydroxyurea was safe and effective in decreasing SCA-related complications in very young children (9-18 months), and largely due to these findings, hydroxyurea is recommended to be offered to all children (≥9 months old) with SCA, independent of disease severity. Nevertheless, children in the treatment arm of BABYHUG continued to experience vaso-occlusive symptoms and to incur organ damage. In clinical trials of older children with SCA, intensification of hydroxyurea to a maximum tolerated dosage (MTD), defined by mild to moderate myelosuppression, may be associated with improved laboratory parameters compared to fixed lower-dosing, but the clinical benefits gained from dose intensification have not been described. Therefore, in this trial, children in the standard treatment arm will receive a fixed dose of hydroxyurea (20 mg/kg/day), and participants in the experimental arm will receive hydroxyurea intensified to MTD, defined by a goal absolute neutrophil count (ANC) of 1500-3000 cells/µL. This trial aims to establish a multicenter infrastructure that will identify, enroll and randomize very young children (9-36 months) to receive fixed dose versus intensified-dose hydroxyurea in a single blinded manner, and to obtain prospective pilot data comparing the clinical and laboratory outcomes between the treatment arms to facilitate design of a definitive phase III trial.

All participants will initially receive hydroxyurea at a dose of \~20 mg/kg/day in an open label fashion for eight weeks (± 2 weeks) prior to randomization. Participants will receive monthly medical evaluations (every 4 ± 2 weeks) where they will have height and weight measurements, medical history, physical examination, and medication adherence assessments. During these monthly visits complete blood counts with absolute reticulocyte count will be monitored. Hemoglobin electrophoresis, complete serum chemistries, urinalysis, lactate dehydrogenase and quality of life measurements will be obtained every 20 (±2) weeks. Transcranial Doppler (TCD) ultrasound velocities will be obtained at study entry (in participants ≥2 years of age) and study exit. Participants randomized to receive hydroxyurea at MTD will have their dose increased by 5 mg/kg/day every 8 weeks, in the absence of toxicity, until a goal ANC of 1500-3000 cells/µL is achieved, up to a maximum of 35 mg/kg/day.

Both groups will receive their assigned treatment for 48 weeks (± 3 weeks). Participants will be in the study for a total of 56 weeks (± 3 weeks) and have 14 clinic visits to the St. Jude outpatient Hematology Clinic during that time. After the 56 weeks, participants will be followed for an additional 30 days for side effects and will then be taken off study.

Eligibility Criteria:
Inclusion Criteria:

* Children with HbSS or sickle hemoglobin (HbS)/β\^0thalassemia
* ≥9 to ≤ 36 months of age at study initiation
* Enrollment will occur irrespective of clinical severity

Exclusion Criteria:

Permanent:

* Receiving chronic red blood cell transfusion therapy.
* Condition or chronic illness, which in the opinion of the PI makes participation unsafe.

Transient (participants may be re-evaluated after ≥14 days):

* Recent (\<30 days) participation in another clinical intervention trial utilizing an investigational new drug/investigational device exemption (IND/IDE) agent.
* Erythrocyte transfusion in the past 2 months.
* Laboratory Assessments:

  * Hemoglobin \<6.0 g/dL
  * Absolute reticulocyte count \<80 \* 10\^3/µL if hemoglobin \<9.0 mg/dL
  * Absolute neutrophil count \<1.5 \* 10\^3/µL
  * Platelet count \<100 \* 10\^3/µL
  * Serum creatinine \> twice the upper limit of normal for age
  * Alanine aminotransferase (ALT) \> twice the upper limit of normal