Hydroxycarbamide (Hydroxyurea)
Hydroxycarbamide
Also known as: Hydrea · Hydroxyurea
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Polycythaemia vera, chronic myeloid leukaemia, mast cell tumours, meningiomas | See Appendix for chemotherapy protocols | PO | variable | Reduce dosage frequency once in remission | 🌍 EU |
- Polycythaemia vera, chronic myeloid leukaemia, mast cell tumours, meningiomas: Perform haematology initially weekly for one month, then every two weeks for one month, then monthly if tolerated.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Polycythaemia vera, chronic myeloid leukaemia | See Appendix for chemotherapy protocols | PO | variable | Reduce dosage frequency once in remission | 🌍 EU |
- Polycythaemia vera, chronic myeloid leukaemia: 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.
Overview
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 of action
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.
Safety & warnings
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)
Precautions
Cytotoxic Handling: Must be handled with appropriate precautions (gloves, avoiding splitting/crushing).
- Feline Sensitivity: Cats are at greater risk of myelosuppression compared to dogs; weekly haematology is mandatory at the start of therapy.
- Renal Impairment: Use with caution in patients with renal dysfunction; dose reduction may be required.
- Other Cautions: Use cautiously in patients with a history of urate stones, or those that have received previous chemotherapy and/or radiotherapy.
Drug interactions
Increased risk of severe bone marrow suppression
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.
Available products
Formulations
- 100 mg tablet
- 1 g tablet
- 300 mg capsule
- 500 mg capsule
Human-labeled
- Hydrea 500 mg capsule
- 100 mg tablet
- 300 mg capsule
- 1 g tablet
Regulatory status
POM (Prescription Only Medicine)
POM (Prescription Only Medicine)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in a tightly closed container according to manufacturer guidelines. Handle as a hazardous/cytotoxic drug.
Client information
- Cytotoxic Drug Warning: This is a chemotherapy medication. Always wear disposable gloves when handling the medication and when cleaning up your pet's urine, faeces, or vomit for at least 48 hours after administration.
- Do not crush or open capsules/tablets.
- Monitoring is Critical: Strict adherence to the blood testing schedule is essential to prevent life-threatening drops in white blood cells.
- Contact your veterinarian immediately if your pet shows signs of extreme lethargy, unexplained bruising/bleeding, vomiting, diarrhoea, or loss of appetite.
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.