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The Pediatric Hydroxyurea Phase 3 Clinical Trial (BABY HUG) was a phase 3 multicenter, randomized, double-blind, placebo-controlled clinical trial of hydroxyurea in infants (beginning at 9-18 months of age) with sickle cell anemia. An important secondary objective of this study was to compare clinical events between the hydroxyurea and placebo groups. One hundred and ninety-three subjects were randomized to hydroxyurea (20 mg/kg/d) or placebo; there were 374 patient-years of on-study observation. Hydroxyurea was associated with statistically significantly lower rates of initial and recurrent episodes of pain, dactylitis, acute chest syndrome, and hospitalization; even infants who were asymptomatic at enrollment had less dactylitis as well as fewer hospitalizations and transfusions if treated with hydroxyurea. Despite expected mild myelosuppression, hydroxyurea was not associated with an increased risk of bacteremia or serious infection. These data provide important safety and efficacy information for clinicians considering hydroxyurea therapy for very young children with sickle cell anemia. This clinical trial is registered with the National Institutes of Health (NCT00006400, www.clinicaltrials.gov).

We evaluated spleen function in 193 children with sickle cell anemia 8 to 18 months of age by 99mTc sulfur-colloid liver-spleen scan and correlated results with clinical and laboratory parameters, including 2 splenic biomarkers: pitted cell counts (PIT) and quantitative Howell-Jolly bodies (HJB) enumerated by flow cytometry. Loss of splenic function began before 12 months of age in 86% of infants in association with lower total or fetal hemoglobin and higher white blood cell or reticulocyte counts, reinforcing the need for early diagnosis and diligent preventive care. PIT and HJB correlated well with each other and liver-spleen scan results. Previously described biomarker threshold values did define patients with abnormal splenic function, but our data suggest that normal spleen function is better predicted by PIT of ≤ 1.2% or HJB ≤ 55/106 red blood cells and absent function by PIT ≥ 4.5% or HJB ≥ 665/106. HJB is methodologically advantageous compared with PIT, but both are valid biomarkers of splenic function. This trial was registered at www.clinicaltrials.gov as #NCT00006400.

Abstract 8 The laboratory and clinical benefits of hydroxyurea therapy for children with sickle cell anemia (SCA) are well recognized, but treatment in young patients is limited in part by concerns about long-term genotoxicity, and specifically possible carcinogenicity. To date, few prospective data have been available to assess the mutagenic and carcinogenic potential of hydroxyurea in young patients with SCA. The Pediatric Hydroxyurea Phase III Clinical Trial (BABY HUG) was a multi-center double-blinded placebo-controlled randomized clinical trial (NCT00006400) testing whether hydroxyurea could prevent chronic organ damage in very young patients with SCA. BABY HUG was conducted across 14 centers and was approved by the local institutional review boards of all participating centers. A total of 193 infants (mean 13.6 months) with SCA (HbSS or HbS/ß°-thalassemia) were randomized to receive hydroxyurea (fixed dose of 20 mg/kg/day) or placebo for two years. An important secondary objective of the study was the in vivo measurement of acquired genotoxicity using three laboratory assays: chromosomal karyotype including quantitation of chromosomal breaks, chromatid breaks, and fusion events; illegitimate VDJ recombination events representing inversion events on chromosome 7 with juxtaposition of T-cell receptor Vg and Jb and gene loci; and micronucleated reticulocyte formation signifying aberrant erythroid production. Subjects in both the hydroxyurea and placebo groups had significantly increased numbers of total chromosome breaks and similar numbers of chromatid breaks at study exit compared to study entry. However, at study exit, subjects with hydroxyurea exposure had similar numbers of chromosome and chromatid breaks as subjects receiving placebo (0.5 ± 1.4 chromosome breaks per 100 metaphases vs. 0.4 ± 2.5, p=NS; 0.6 ± 1.1 chromatid breaks per 100 metaphases vs.0.8 ± 3.4, p=NS). There were no changes in the number of illegitimate VDJ recombination events observed, comparing study entry and exit samples either in the hydroxyurea or the placebo treatment group. At study exit, subjects treated with hydroxyurea had similar numbers of illegitimate VDJ recombination events as subjects receiving placebo (0.7 ± 0.5 events per μg of DNA versus 0.7 ± 0.4 events, p=NS). Subjects treated with hydroxyurea had a similar number of early reticulocytes containing micronuclei at study exit compared to subjects receiving placebo (0.3 ± 0.2% versus 0.3 ± 0.2%, p=NS). Together, these data indicate that hydroxyurea treatment in very young patients with SCA was not associated with any significant increases in genotoxicity compared to placebo treatment. These data provide evidence of cytogenetic stability in this susceptible population of young children and contribute to a growing body of evidence to suggest that in vivo genotoxicity of hydroxyurea in patients with SCA appears to be low. Disclosures: Dertinger: Litron Laboratories: Employment.

Abstract 171 Background: The BABY HUG trial was a multi-center double-blinded randomized comparison of hydroxyurea (HU) versus placebo in infants (mean age 13.6 mo. at entry) with HbSS/Sβ° thalassemia who were followed for 2 years [Lancet 377(2011):1663–1672; Clinical Trials #NCT00006400]. Hydroxyurea therapy was associated with less pain, dactylitis, acute chest syndrome (ACS), hospitalization (HSN), and transfusion (TX) and with improved hematologic values; toxicity was limited to mild-moderate neutropenia. On the basis of the safety and efficacy data from this trial, it was concluded that hydroxyurea therapy can be considered for all very young children with sickle cell anemia (SCA). With anticipated broader use of hydroxyurea in this population, we examined estimated medical costs of care (based on Medicaid reimbursement) in treated versus placebo subjects. Methods: The BABY HUG database (C-TASC, Baltimore, MD) was utilized to compare inpatient events in subjects receiving hydroxyurea with those receiving placebo. Unit costs were estimated from the 2009 Thomson Reuters MarketScan® Multi-state Medicaid Database for children with HbSS (ICD-9 codes 282.61 or 282.62), ages 1–3 years. Inpatient costs included emergency department (ED) costs for admissions from an ED in about 80% of the 748 admissions in the database. Inpatient cost estimates were based on length of stay (LOS) modified by a diagnosis of ACS or splenic sequestration (SpS) or a procedure code for a TX. Outpatient expenses were estimated based on the schedule required for BABY HUG (and recommended for clinical use) and a “standard” schedule for 1–3 year-olds with SCA based on management protocols at 3 pediatric sickle cell centers in the US. Results: 96 subjects were randomized to hydroxyurea (83 completed the trial); 97 received placebo (84 completed the trial). In the full study, there were 232 hospitalizations (for any cause) in those receiving hydroxyurea and 324 in those on placebo; inpatient data were captured for only the final 77% of admissions (between 2/06 and 9/09). The LOS for subjects receiving hydroxyurea (mean 3.7, median 3, range 1–9 days) did not differ from those receiving placebo (3.6, 3, 1–13). Estimated inpatient and outpatient costs are shown in Tables 1 and 2. When inpatient and outpatient expenses were combined, the annual cost for 1–3 year-old children with SCA was $11,345 on hydroxyurea and $14,815 on placebo, a difference of $3,470. Discussion/Conclusion: Despite increased outpatient care expenses from clinic visits, laboratory monitoring, and hydroxyurea, savings on inpatient care resulted in an overall reduction in estimated annual per patient expenditure of approximately 23%. A limitation of our analysis was the dependence on MarketScan Medicaid data in lieu of the availability of specific expenses of the subjects participating in the BABY HUG study. Medicaid data may understate costs of care; based on prior analyses, we estimate that costs to private payers may be 20–30% greater than Medicaid reimbursements. We conclude that increased use of hydroxyurea treatment in children with SCA can lead to significant medical cost savings. Disclosures: Off Label Use: Hydroxyurea is not indicated for treatment of children with sickle cell disease. Use of this medication was for clinical indications and not mandated by this observational study.

Abstract 2134 BABY HUG randomly assigned children with sickle cell anemia ages 9 to 18 months at entry to a two-year double-masked treatment course of 20 mg/kg/d of hydroxyurea (HU) or placebo (PBO). The primary goal of this clinical trial was to determine if treatment with HU could reduce organ damage or dysfunction (spleen function assessed by 99mTc-sulfur colloid and renal function by 99mTc-DTPA clearance) by 50%. Children were seen at least monthly for blood and clinical evaluations. [Lancet 2011; 377(9778):1663–1672.] Between March 23, 2006 and June 1, 2006, the BABY HUG study was placed on “clinical hold” due to the omission of an expiration date on the treatment label for one lot of the study treatments. During the clinical hold, there were 94 children on active study treatment (47 HU, 47 PBO); four and six children, respectively, had finished their two-year follow up. Subjects continued regular visits and clinical event monitoring but received no study medication. To examine the impact of the clinical hold on toxicity and clinical events, the BABY HUG study period was divided into three intervals: Before, During, and After the clinical hold. Each period was offset by a one-month delay from the actual onset and end date to allow for wash-out and wash-in periods surrounding the clinical hold. The clinical hold produced both hold effects (effects produced by the hold that were consistent in the two treatment groups) and treatment-hold interaction effects (hold effects that were different by treatment). The interaction effects are presented below. The table presents the rate or prevalence of selected clinical events during each interval. The rate of pain, one of the clinical events shown to benefit from treatment with HU, was comparable to the PBO rate during the clinical hold but was significantly lower in the pre- and post-hold intervals. The prevalence of splenomegaly (defined by palpation ≥2 cm below the costal margin), which was slightly greater in the HU group than in the PBO group during the pre- and post-hold intervals, increased to a four-fold difference during the clinical hold. There was no difference between the groups in the rate of splenic sequestration in any interval.Clinical Events Before, During and After Clinical Hold+Before HoldDuring HoldAfter HoldHU 55.1*PBO 50.3*HU 8.3*PBO 7.8*HU 125.1*PBO 126.8*AENo.RateNo.RateNo.RateNo.RateNo.RateNo.RateDactylitis59.13467.6112.0338.51814.48667.8Pain3461.772143.114168.715192.3129103.1288227.1Splenomegaly^3054.42039.814168.7338.58366.36551.6Lab ResultsMeanMeanMeanMeanMeanMeanRetic Ct (k/mm3)191.5329.4300.5327.3237.0335.4Hgb (gm/dL)10.078.699.098.739.288.69MCV (fL)86.8481.9082.8279.8585.0080.00+Rates in bold are significantly different at p < 0.05 within each time period*Person Years of Exposure^Prevalence Hematologic changes showing a treatment-period interaction included a significantly larger difference in absolute reticulocyte count between the HU and placebo group During the Hold as compared to Before and After. The HU-induced increase in Hb and MCV was significantly diminished During the Hold. All measurements moved back towards their pre-hold differences after the hold was lifted. The clinical hold in BABY HUG provided an unforeseen opportunity to study the clinical and laboratory impact of cessation of HU therapy for a brief time period. No serious clinical effects or toxicities occurred during the clinical hold, perhaps due to its limited time span. Parents and physicians should be aware that stopping HU therapy may result in increased episodes of pain or splenic enlargement. Disclosures: Off Label Use: Hydroxyurea which is not approved for use in children with sickle cell disease. Casella:Adventrix: Honoraria.

The dose-response relationship between extracellular concentration of cytosine arabinoside (ara-C) and intracellular formation of the putative active metabolites of ara-C [ara-C incorporation into DNA and intracellular pools of ara-C in triphosphate form (ara-CTP)] was investigated in blast cells obtained from patients with acute nonlymphocytic leukemia (ANLL) by exposing these cells in vitro to 10, 100, or 1,000 nmol/L of ara-C. We studied 23 untreated patients who subsequently achieved complete remission (CR) with a regimen using daunorubicin and conventional doses of ara-C (ara-C-sensitive group), and 30 patients judged to be ara-C-resistant either by failing initial induction therapy (16 patients) or by having relapsed on an ara-C- containing maintenance regimen (14 patients). In both patient groups, ara-C incorporation into DNA and intracellular ara-CTP both displayed statistically significant increases in response to increasing extracellular concentrations of ara-C (P = .0001 in both cases), with the rate of increase of ara-CTP greater than that of ara-C incorporation. Moreover, blast cells from all patients, even those who were most clinically resistant to ara-C, were able to form ara-CTP and to incorporate ara-C into DNA. Each tenfold increment in extracellular ara-C concentration caused an 8.5-fold increase in ara-CTP, but only a 3.6-fold increase in ara-C incorporation into DNA. Thus, the efficiency of incorporation of ara-C into DNA (defined as the ratio of ara-C incorporation to ara-CTP pools) decreased by 58% with each tenfold increment in the extracellular concentration of ara-C (P less than .0001), presumably as a result of the inhibitory effect of ara-CTP on DNA polymerase. Using an analysis of covariance, modest differences were found in the levels of the ara-C metabolite variables in the ara-C- sensitive group as compared with the resistant group. However, because there was considerable overlap in ara-C metabolite formation among the patient groups, it was not possible to predict clinical outcome by these in vitro assessments of ara-C metabolism.