Hydroxyurea Dosing in Sickle Cell Anemia

Introduction to Hydroxyurea Therapy

The American College of Hematology recommends hydroxyurea be administered once daily by mouth, starting with an initial dose of 15-20 mg/kg/day, with subsequent titration to achieve the maximum tolerated dose (MTD) of 20-35 mg/kg/day based on hematologic response and patient tolerance 1

The National Institutes of Health guidelines suggest that children (≥9 months) and adults initiate hydroxyurea at 15-20 mg/kg/day as a single daily dose 1
Hydroxyurea is available in capsule, rapid-dissolving tablet, or liquid formulation compositions 1

The European Hematology Association recommends that children from 9 months of age with HbSS or Sβ0-thalassemia receive hydroxyurea even without clinical symptoms 1
For patients with chronic kidney disease and progressive anemia, consider combined therapy with erythropoiesis-stimulating agents, maintaining hemoglobin ≤10 g/dL to reduce the risk of vaso-occlusive complications 2, 3

The American Society of Hematology notes that myelosuppression is the most common dose-limiting toxicity, but typically resolves within 2 weeks after temporary suspension of the medication 1, 4
If severe myelosuppression occurs (decrease in one or more cell lines), temporarily suspend hydroxyurea 4, 3

In hyperleukocytosis (leukocytes >100 × 10⁹/L), use hydroxyurea at doses of up to 50-60 mg/kg/day until leukocytes are reduced to <10-20 × 10⁹/L 5

Do not suspend hydroxyurea when initiating doxycycline or other antibiotics 4
Hydroxyurea should be suspended ≥72 hours before CAR-T cell infusion if the patient is on a transplant protocol 6
The medication has an established safety profile without increased risk of congenital defects, infections, stroke, or neoplasias in long-term follow-up 1, 4

The American Academy of Pediatrics recommends hydroxyurea is available as capsules, fast-dissolving tablets, or compounded liquid formulations to facilitate administration across age groups 7

Bone marrow suppression is the primary dose-limiting toxicity but is manageable and reversible, according to the American Thoracic Society 7, 8
Severe neutropenia (absolute neutrophil count <500/mm³) is rare and has not been complicated by infection in clinical trials, as reported by the American Thoracic Society 8

Hydroxyurea reduces vaso-occlusive pain crises, acute chest syndrome episodes, hospitalizations, and transfusion requirements by approximately 50%, as stated by the American Thoracic Society 8
Prolonged therapy (≥5 years) is necessary to achieve mortality benefit, with 17-year data showing 30.4% vs 51.1% mortality in those receiving ≥5 years of therapy versus <5 years, according to the American Thoracic Society 8

For patients with increased mortality risk, hydroxyurea is strongly recommended regardless of hemoglobin level, as stated by the American Journal of Respiratory and Critical Care Medicine 9
When combining hydroxyurea with erythropoiesis-stimulating agents in patients with chronic kidney disease and worsening anemia, maintain hemoglobin ≤10 g/dL to reduce risk of vaso-occlusive complications, stroke, and venous thromboembolism, as advised by the American Society of Hematology 10
Mild to moderate neutropenia occurs commonly and requires dose reduction but not discontinuation, with a frequency of 47% of patients, according to the American Journal of Respiratory and Critical Care Medicine 9

The American Society of Hematology advises a conservative hemoglobin threshold of ≤10 g/dL when combining hydroxyurea with erythropoiesis-stimulating agents to prevent hyperviscosity complications 10
ESAs allow more aggressive hydroxyurea dosing by counteracting treatment-related anemia, but the hemoglobin ceiling prevents hyperviscosity complications, as stated in Blood advances 10