The Hydroxyurea Absorption Phenotype: A Key PK/PD Determinant in Sickle Cell Disease Treatment

Area of Science:

• Pharmacology
• Hematology
• Clinical Pharmacy

Background:

• Hydroxyurea (HU) is a primary treatment for sickle cell disease (SCD).
• Significant inter-individual variability in HU's pharmacokinetic/pharmacodynamic (PK/PD) properties is observed.
• The factors driving this variability are not fully understood.

Purpose of the Study:

• To develop a population PK model for HU using data from the OPTIMDREP trial.
• To quantify variability in HU PK parameters.
• To identify covariates influencing HU PK and hematological response in SCD patients.

Main Methods:

• Non-compartmental analysis (NCA) and nonlinear mixed-effects modeling (NLME) were applied to plasma samples from 22 SCD patients.
• Covariates influencing PK variability and PK/PD correlations with hematological parameters (MCV, reticulocytes, HbF%, neutrophils) were investigated.
• The study utilized data from the OPTIMDREP randomized trial (NCT06464458).

Main Results:

• NCA identified two distinct HU absorption phenotypes: rapid and slow.
• The absorption phenotype was confirmed as a key covariate for absorption rate (k a), explaining 50% of its inter-individual variability.
• Rapid absorbers demonstrated superior responses in MCV, reticulocyte counts, and a trend towards higher HbF% compared to slow absorbers, without increased toxicity.

Conclusions:

• The absorption phenotype is a novel covariate that significantly impacts HU PK and predicts a superior erythropoietic response in SCD patients.
• Integrating absorption phenotype into PK-guided dosing algorithms can optimize HU therapy personalization.
• This approach may improve early-response biomarker monitoring and enhance treatment efficacy for SCD.