Efficacy of Hydroxyurea To Prevent Organ Damage in Young Children with Sickle Cell Anemia.
Authors: Thornburg Courtney D. , Dixon Natalia , Burgett Shelly , Mortier Nicole A. , Zimmerman Sherri A. , Bonner Melanie J. , Calatroni Agustin , Ware Russell E. 
Published: October 2019

Abstract
Hydroxyurea (HU) prevents many acute complications of sickle cell anemia (SCA) in adults and children, but its potential to delay or prevent chronic organ damage has not been defined. The objectives of this prospective IRB-approved study were to assess the safety and efficacy of HU in young children with SCA (age 18 mon–5 years) and to determine whether 2 years of therapy preserves renal function, reduces transcranial doppler ultrasound (TCD) values, and prevents development of brain ischemia as evidenced by magnetic resonance imaging/angiography (MRI/MRA). Fourteen children with SCA (11 male, 3 female; mean age 35±11 mon) enrolled and underwent evaluation including blood counts, %HbF measurement, determination of the glomerular filtration rate (GFR) by radionuclide DTPA clearance and Schwartz estimate, TCD mean cerebral artery (MCA) velocities, and brain MRI/MRA. HU was started at 20 mg/kg/day and escalated by 5mg/kg/day every 8 weeks to a maximum tolerated dose (MTD) or 30 mg/kg/day (mean dose 28±4 mg/kg). Children were evaluated initially every 4 weeks. All baseline tests were repeated at study exit (mean time 25±3 months). HU was tolerated well by all children. Hematological changes occurred as expected, with significant increases observed in hemoglobin concentration, MCV, and %HbF and significant decreases in reticulocytes, WBC, and neutrophils. The average GFR value did not rise as expected in this age range; the DTPA GFR decreased by 5.1 mL/min/1.73 m2 (p=0.26) with only 3 of 11 exit studies exceeding 150 mL/min/1.73 m2 and the Schwartz estimate increased by 16.5 mL/min/1.73 m2 (p=0.17). During HU therapy, the average TCD values significantly decreased with a mean decrease of 26±28 cm/sec in the right MCA (p<.01) and mean decrease of 27±33 in the left MCA (p<.05). At study entry, 3 children had conditional TCD velocities, but all were normal at study exit. One child had mild small vessel ischemic changes on MRI at study entry that were unchanged at study exit. Two children had mild MRA changes that were stable or improved at the end of the study. All children had normal or improved rates of growth and development during therapy. Two children required PRBC transfusion for acute events (acute chest syndrome and hypoplastic anemia during a viral illness). There was one episode of Moraxella catarrhalis bacteremia that was unrelated to myelosuppression and responded to antibiotic therapy. One child was removed from study at week 82 due to the development of thrombocytopenia and hypersplenism, another had acute splenic sequestration but continued HU without recurrence, and a third child with previous acute splenic sequestration did not have recurrence during the study. In conclusion, HU therapy appears to be well tolerated in young children with SCA. In addition to providing beneficial changes in hematological parameters, HU has salutary effects on both the kidney and brain. HU therapy was associated with a stable GFR value during a time interval when hyperfiltration develops, and led to significant decreases in TCD velocities. However, preservation of splenic tissue could lead to an increased risk of splenic complications. Follow-up studies are warranted to determine if long-term HU therapy can preserve or restore organ function in this patient population.