Evidence Highlights the Importance of Hydroxyurea Adherence in Children

Sarah Reeves, PhD, MPH

Credit: CHEAR Michigan Medicine

Results from a recent study indicate that a high level of adherence is essential to achieve a lower incidence of common negative clinical outcomes among children with sickle cell anemia taking hydroxyurea. The median adherence level in the study population was 53%, suggesting moderate and severe hydroxyurea nonadherence may be more common than previously appreciated.¹

Hydroxyurea, a medication that increases the production of fetal hemoglobin, has been a first-line therapy for sickle cell disease (SCD) and anemia for decades, approved by the US Food and Drug Administration (FDA) for treating adult patients in 1998, and later, for treating pediatric patients in 2017.²

The medication has been shown to decrease the incidence of vaso-occlusive pain crises (VOC) and acute chest syndrome among children with sickle cell anemia. However, adherence to hydroxyurea is essential to achieve optimal clinical outcomes.¹

Analyzing Treatment Adherence in Pediatric Patients

Sarah Reeves, PhD, MPH, Department of Pediatrics, Susan B Meister Child Health Evaluation and Research (CHEAR) Center, University of Michigan, and a team of investigators aimed to assess the relationship between levels of adherence to hydroxyurea and clinical outcomes among children and adolescents with sickle cell anemia in a retrospective cohort study.

In the investigation, Medicaid data from 6 US states, covering a period from 2005-2012 were analyzed. The study population consisted of children aged 1-17 years with sickle cell anemia enrolled in Medicaid for at least 3 years.

When examining the number of children that initiated hydroxyurea, the medication possession ratio was calculated as the proportion of days covered by hydroxyurea. The clinical outcomes assessed included the number of VOC-related inpatient admissions, emergency department (ED) visits, as well as encounters with acute chest syndrome.

The team implemented Multivariable Poisson models to predict outcomes by medication possession ratio quartile, adjusting for previous healthcare utilization, state, and age.

Hydroxyurea Treatment Adherence Impacts Clinical Outcomes

Results revealed that hydroxyurea was initiated by 515 children, with a median medication adherence of 53%, though this level varied widely (IQR: 0.3-0.8). The annual median number of visits for acute chest syndrome was 0.0, 1.3 for VOC-related emergency department, and 1.4 for VOC-related inpatient admissions.

With a high level of adherence (<75%) children were less likely to experience VOCs and acute chest syndrome compared with children who had lower adherence levels. This difference was significant for acute chest syndrome visits when compared with the lowest quartile.

For each outcome assessed, the group of children with the highest quartile of medication possession ratio had the fewest predicted incidents of the negative clinical outcomes being measured in the study.

Investigators noted some study limitations, such as the use of administrative claims data, which may not capture all relevant clinical information. The study only included Medicaid-enrolled children, which isn’t entirely representative of the overall sickle cell anemia population.

Despite these limitations, they wrote that these findings suggest healthcare providers should prioritize adherence monitoring and interventions, for children who take hydroxyurea, in order to achieve optimal clinical outcomes.

The team also emphasized the need for further research to identify, develop, and test innovative strategies to promote adherence and improve clinical outcomes among these children.

References:

1. Reeves SL, Dombkowski KJ, Peng HK, et al. Adherence to hydroxyurea and clinical outcomes among children with sickle cell anemia [published online ahead of print, 2023 Apr 12]. Pediatr Blood Cancer. 2023;e30332. doi:10.1002/pbc.30332
2. Hydroxyurea for Sickle Cell Disease. Treatment Information from the American Society of Hematology. Accessed April 20, 2023. https://www.hematology.org/-/media/Hematology/Files/Education/Hydroxyurea-Booklet.pdf