Hydroxycarbamide (Hydroxyurea)
Hydroxycarbamide (commonly known as hydroxyurea) is an antimetabolite antineoplastic agent. It is primarily used in veterinary medicine for the treatment of myeloproliferative disorders such as **polycythaemia vera** and **leukaemias**, as well as for **mast cell tumours** and as an adjunctive treatment for **canine meningiomas**. > **WARNING**: This is a cytotoxic drug. Strict safety and handling protocols must be followed to prevent human exposure. **Clinical Pearl:** Cats are significantly more sensitive to the myelosuppressive effects of hydroxycarbamide and require more intensive initial monitoring.
Mechanism: Hydroxycarbamide inhibits the enzyme **ribonucleotide reductase** → prevents the conversion of ribonucleotides to deoxyribonucleotides → depletes the intracellular pool of precursors essential for **DNA synthesis and repair**. It is a cell-cycle specific agent acting primarily in the **S-phase**, but it may also arrest cells at the G1-S border.
Dosing by species
- Polycythaemia vera, chronic myeloid leukaemia, mast cell tumours, meningiomas · See Appendix for chemotherapy protocols · PO · variable · Reduce dosage frequency once in remission · Perform haematology initially weekly for one month, then every two weeks for one month, then monthly if tolerated.
- Polycythaemia vera, chronic myeloid leukaemia · See Appendix for chemotherapy protocols · PO · variable · Reduce dosage frequency once in remission · Haematology MUST be monitored weekly at the start of drug therapy due to greater risk of myelosuppression.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Pre-existing bone marrow suppression
Adverse effects
- Myelosuppression (dose-limiting)
- Nausea
- Vomiting
- Diarrhoea
- Anorexia
- Dysuria
- Stomatitis
- Sloughing of nails
- Alopecia
- Methaemoglobinaemia (in cats at high doses)
- Cardiovascular changes (increased diastolic BP/HR, decreased systolic BP)
Drug interactions
- Other myelosuppressive agents · Increased risk of severe bone marrow suppression · major
Monitoring
- Haematology (weekly for 1 month, then biweekly for 1 month, then monthly)
- Renal function parameters
- Blood pressure and ECG (due to potential cardiovascular effects)
Overdose
In cats, very high doses (>500 mg) have been reported to cause **methaemoglobinaemia**.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.