Hydreasyn (Hydroxycarbamide)

Hydreasyn is indicated for the management of several chronic blood disorders where reduction of abnormal cell proliferation is required.

• Sickle cell disease, to reduce the frequency of painful vaso‑occlusive crises.
• Chronic myelogenous leukemia (CML), as part of disease‑modifying therapy.
• Polycythemia vera, to control elevated red‑cell mass.
• Essential thrombocythemia, to lower platelet counts.
• Off‑label use in certain myeloproliferative neoplasms under specialist supervision.

• Hydroxycarbamide inhibits the enzyme ribonucleotide reductase, which is essential for converting ribonucleotides to deoxyribonucleotides. By limiting the pool of deoxyribonucleotides, the drug decreases DNA synthesis and slows the replication of rapidly dividing cells, particularly abnormal hematopoietic cells. This antimetabolic action underlies its cytoreductive and antineoplastic effects in the indicated blood disorders. The inhibition is dose‑dependent and results in a reversible S‑phase cell‑cycle arrest, allowing normal marrow recovery while suppressing malignant clones.

Hydroxycarbamide may cause a range of adverse reactions, varying from mild to severe.

Common

• Nausea, vomiting, or loss of appetite that may affect nutrition.
• Skin hyperpigmentation, often appearing as a brownish discoloration on the palms, soles, or nails.
• Mild, reversible reduction in white‑blood cell (leukocyte) counts, typically detected in routine labs.
• Temporary thinning or loss of hair, which usually regrows after discontinuation.

Serious

• Significant neutropenia or agranulocytosis, increasing susceptibility to bacterial and fungal infections.
• Acute hemolytic episodes in individuals with glucose‑6‑phosphate dehydrogenase (G6PD) deficiency.
• Development of pulmonary arterial hypertension, presenting with shortness of breath and fatigue.
• Renal dysfunction manifested by rising serum creatinine or reduced glomerular filtration rate.

Because hydroxycarbamide affects blood cell production and DNA synthesis, several precautions should be observed before and during therapy.

• Perform baseline and periodic complete blood counts to monitor for cytopenias.
• Assess renal and hepatic function prior to initiation and at regular intervals.
• Avoid use during pregnancy; the drug is classified as pregnancy category D and may cause fetal harm.
• Counsel women of childbearing potential about effective contraception throughout treatment and for a defined period after discontinuation.
• Use caution in patients with known G6PD deficiency due to risk of hemolysis.
• Monitor for signs of pulmonary hypertension, such as unexplained dyspnea or edema.
• Review any history of malignancies, as the drug may influence tumor dynamics.

Hydroxycarbamide can interact with other medicines, altering its effectiveness or increasing toxicity.

Avoid

• Concurrent use with strong CYP2C9 inhibitors (e.g., fluconazole) that may raise hydroxycarbamide plasma levels.
• Co‑administration with other myelosuppressive agents (e.g., azacitidine, chemotherapy) that can exacerbate bone‑marrow suppression.
• Combining with drugs that increase risk of hemolysis in G6PD‑deficient patients, such as primaquine.

Use with caution

• Anticoagulants (e.g., warfarin) – hydroxycarbamide may affect INR; monitor clotting parameters.
• Allopurinol or febuxostat – may increase risk of hypersensitivity reactions; observe for rash or fever.
• Vaccines containing live attenuated organisms – immunosuppression may reduce vaccine efficacy; consider timing.
• NSAIDs – may worsen renal function when used together; monitor kidney markers.