In oncology pharmacy, hydroxyurea is primarily utilized as a cytoreductive agent to rapidly lower high white blood cell (WBC) counts, often before a definitive treatment plan is established,.
1. Emergency Cytoreduction and Bridging
For patients presenting with “proliferative” leukemias—where the WBC count is extremely high and rising rapidly—hydroxyurea is initiated immediately to mitigate the risk of leukostasis,. This often occurs as a bridge while the medical team waits (typically 3–5 days) for actionable molecular and cytogenetic results, such as FLT3 or IDH1/2 status, which dictate the definitive induction regimen,.
2. Management of Targeted Therapy Side Effects
Hydroxyurea plays a specific role in managing complications from newer targeted agents:
- IDH Inhibitors: Targeted therapies like ivosidenib or enasidenib can cause rapid myeloid proliferation and differentiation syndrome,. If the WBC count exceeds 30,000 cells/µL during treatment with these inhibitors, hydroxyurea is started to control the count.
- Differentiation Syndrome in APL: In cases of Acute Promyelocytic Leukemia (APL), if differentiation syndrome is difficult to treat with corticosteroids alone, cytotoxic agents like hydroxyurea may be added to the regimen,,.
3. Palliative and Supportive Care
In patients who are not candidates for intensive or low-intensity curative chemotherapy (e.g., those with an ECOG performance status of 3 or 4), hydroxyurea is used as part of “best supportive care”,. In this context, it is titrated specifically to control leukocytosis and prevent the symptoms associated with high blast counts without the goal of achieving complete remission,.
4. Clinical Considerations for the Pharmacist
- Dosing: It is typically administered orally, with doses adjusted based on the patient’s daily WBC count.
- Goal: Unlike intensive induction, which aims for complete marrow clearance, hydroxyurea is used to keep the patient stable and prevent vascular complications from high cell viscosity.