Hydroxyurea pharmacokinetics and precision dosing in low-resource settings.

Hydroxyurea is effective disease-modifying treatment for sickle cell anemia (SCA). Escalation to maximum tolerated dose (MTD) achieves superior benefits without additional toxicities, but requires dose adjustments with serial monitoring. Pharmacokinetic (PK)-guided dosing can predict a personalized optimal dose, which approximates MTD and requires fewer clinical visits, laboratory assessments, and dose adjustments. However, PK-guided dosing requires complex analytical techniques unavailable in low-resource settings. Simplified hydroxyurea PK analysis could optimize dosing and increase access to treatment. Concentrated stock solutions of reagents for chemical detection of serum hydroxyurea using HPLC were prepared and stored at -80C. On the day of analysis, hydroxyurea was serially diluted in human serum, then spiked with N-methylurea as an internal standard and analyzed using two commercial HPLC machines: 1) standard benchtop Agilent with 449 nm detector and 5 micron C18 column; and 2) portable PolyLC with 415 nm detector and 3.5 micron C18 column. After validation in the United States, the portable HPLC and chemicals were transported to Tanzania. A calibration curve using hydroxyurea 2-fold dilutions ranging from 0 to 1000 µM was plotted against the hydroxyurea:N-methylurea ratio. In the United States, both HPLC systems yielded calibration curves with R > 0.99. Hydroxyurea prepared at known concentrations confirmed accuracy and precision within 10%-20% of the actual values. Both HPLC systems measured hydroxyurea with <10% variance from the prepared concentrations, and paired analysis of samples on both machines documented <15% variance. Serial measurements of 300 and 100 μM concentrations using the PolyLC system were precise with 2.5% coefficient of variance. After transport to Tanzania with setup and training, the modified PolyLC HPLC system produced similar calibration curves with R > 0.99. Increasing access to hydroxyurea for people with SCA requires an approach that eases financial and logistical barriers while optimizing safety and benefits, especially in low-resource settings. We successfully modified a portable HPLC instrument to quantify hydroxyurea, validated its precision and accuracy, and confirmed capacity building and knowledge transfer to Tanzania. HPLC measurement of serum hydroxyurea is now feasible in low-resource settings using available laboratory infrastructure. PK-guided dosing of hydroxyurea will be tested prospectively to achieve optimal treatment responses.