Impact of hydroxyurea dose and adherence on hematologic outcomes for children with sickle cell anemia

Hydroxyurea is the primary treatment for sickle cell anemia (SCA), yet real-world implementation in high-income settings is suboptimal. Variation in prescribed hydroxyurea dose and patient adherence in these settings can both affect actual exposure to hydroxyurea. Quantifying the contributions of hydroxyurea dose and medication adherence to the relationship between hydroxyurea exposure and hematologic parameters could inform strategies to optimize exposure and improve outcomes.

We evaluated the relationship between hydroxyurea exposure, defined by average prescribed dose and adherence, and hematologic parameters using data from children with SCA who were enrolled in two prospective hydroxyurea adherence studies. Hydroxyurea adherence was assessed by video directly observed therapy or electronic pill bottle and medication administration record. Average prescribed dose was abstracted from prescriptions in patients' electronic medical record. Participants with a hydroxyurea exposure >20 mg/kg/day and ≤20 mg/kg/day were included in the higher and lower exposure groups, respectively.

Forty-five participants were included in the analysis (56% male; median age 12 years [range 2-19]; 98% Black). Higher exposed participants (n = 23) were prescribed a higher dose (27.2 vs. 24.4 mg/kg/day, p = .002) and had better adherence (0.92 vs. 0.71, p ≤ .001) compared to lower exposed participants (n = 22). Higher exposure was associated with higher fetal hemoglobin (p = .04) and mean corpuscular volume (p = .02).

Higher hydroxyurea exposure is associated with improved hematologic parameters in the high-income setting and is affected by both prescribed dose and adherence. Future studies are needed to optimize both adherence and hydroxyurea prescribing and confirm that increasing exposure improves clinical outcomes in this setting.