Hydroxyurea Treatment of Young Children with Sickle Cell Anemia: Safety and Efficacy of Continued Treatment – the BABY HUG Follow-up Study

Abstract 7

BABY HUG [Clinical Trials #NCT00006400], an NIH-NICHD sponsored randomized placebo-controlled trial showed that hydroxyurea (HU) administered to 9–18 month old children with sickle cell anemia (SCA) provides substantial clinical benefit. Benefits include a decrease in pain crises, acute chest syndrome events, need for transfusion and hospital admission; hematologic improvement include higher total and fetal hemoglobin concentration, larger red cell size, and lower WBC counts with toxicity limited to transient reduction in absolute neutrophil count (ANC) [Lancet 2011; 377:1663–72]. The parent or guardian of all 176 children who completed at least 18 months of randomized treatment were offered participation in an initial observational BABY HUG Follow-Up Study and 163 (93%) consented to participate. Clinical and laboratory data were collected every 6 months by structured abstraction of the medical record regarding use of clinically prescribed HU (dose escalation recommended), blood counts, clinical imaging, and sickle cell-related events. At the time of enrollment the family did not know their child's randomized study treatment assignment; 133 (82%) initially chose clinical prescription of open-label HU. Acceptance of HU has remained high through 36 months of follow-up; during each 6 month data collection period 68–75% of participants reported having taken HU.

Only 2 patients have left the study (due to relocation) and more than 93% of expected data have been collected. Preliminary analyses as of May 2011, including 417 patient years (pt-yrs) of follow up, demonstrate that in comparison to participants not taking HU, children who continue to take HU have statistically lower rates of pain crises requiring emergency department (ED) visits, episodic transfusions, and hospital admissions for any reason, including acute chest syndrome or febrile illness (see table). The substantial decrease in acute chest syndrome episodes is similar to the effect demonstrated with HU use in the randomized BABY HUG trial in younger infants and consistent with published trials detailing the benefit of HU therapy in older children and adults. The decrease in the rate of admission for febrile events in HU-treated patients is also comparable to that in the randomized trial, but the reason for this benefit is uncertain. There was no difference in hospitalization rates for painful events including dactylitis. Two patients in the non-HU group had a stroke. There were no differences between groups in the frequency of a palpable spleen or rate of acute splenic sequestration crises. Through 36 months of follow up children taking HU had persistently higher hemoglobin and MCV, and lower WBC and ANC than those not taking HU.

Results of these analyses including growth and development assessments will enhance our understanding of the impact of HU use in children with SCA starting at a very young age. The accruing data from the BABY HUG Follow-Up Study demonstrate a continuation of the substantial benefits of early HU therapy with no discernable additional toxicities. Ongoing follow up of this cohort is essential to fully define these benefits as children grow, and to observe for late toxicity.