Hydroxycarbamide (Hydroxyurea)

Hydroxycarbamide (Hydroxyurea): Uses, Dosage and Side Effects

Overview

• It inhibits ribonucleotide reductase, which converts ribonucleotides to deoxyribonucleotides (important precursors for DNA synthesis and repair).
• It acts primarily in the S-phase, but may also arrest cells at the G1-S border.

Uses of Hydroxycarbamide (Hydroxyurea)

• Treatment of polycythaemia vera, chronic myeloid leukaemia and chronic granulocytic leukaemia.
• Treatment of mast cell tumours and part of adjunctive treatment of canine meningioma.

Dose of Hydroxycarbamide (Hydroxyurea) in Dogs and Cats

Dogs:

• CML: 50 mg/kg p.o. q24h for 1–2 weeks then q48h.
• Polycythaemia vera or CML: 50–80 mg/kg p.o. q3d or 1 g/m2 p.o. q24h until haematology is normal.
• Mast cell tumours: 60 mg/kg p.o. q24h for 14 days; then 30 mg/kg p.o. q24h.
• Meningioma: 20 mg/kg p.o. q24h or 50 mg/kg p.o. 3 times a week.

Cats:

• 10 mg/kg q12–24h until remission; then taper to lowest effective frequency by monitoring haematocrit; or 25 mg/kg p.o. 3 times a week.
• Meningioma: 20 mg/kg p.o. q24h.

Side Effects of Hydroxycarbamide (Hydroxyurea) in Dogs and Cats

• Myelosuppression.
• GI signs (nausea, vomiting, diarrhoea, anorexia).
• Dysuria.
• Skin reactions (stomatitis, sloughing of nails, alopecia).
• Myelosuppression is dose-limiting; monitor haematological parameters at regular intervals.
• In cats given very high doses (>500 mg) methaemoglobinaemia is reported.
• Normal doses are associated with increased diastolic blood pressure and heart rate but decreased systolic blood pressure, QT and PR intervals, and maximum left ventricular systolic and end-diastolic pressures.

Contraindications of Hydroxycarbamide (Hydroxyurea) in Dogs and Cats

• Patients with bone marrow suppression.
• Use with caution in patients with a history of urate stones, renal disease and those that have received previous chemotherapy and/or radiotherapy.

Some Notes:

• It is advisable not to use it with other myelosuppressive agents.