Hydroxyurea
Hydroxycarbamide
Also known as: Hydrea · Droxia · Mylocel · Dacrodil · Droxiurea · Hydrine · Litalir · Medroxyurea · Neodrea · Onco-Carbide · Oxeron · Syrea · Hydroxycarbamide · Hydroxycarbamidum · NSC-32065 · SQ-1089 · WR-83799
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceMeningioma (extra-label)
Verified clinician required
- q48-72h
NA
Governing clinical context (6)
- NOTE: Hydroxyurea is not commonly used in veterinary medicine, and published dosage recommendations can vary widely.
- Because of the potential toxicity of this drug to patients, veterinary personnel, and clients, and because chemotherapy indications, treatment protocols, monitoring, and safety guidelines often change, the following dosages should be used only as a general guide. 9
- ■ Hydroxyurea is a type of chemotherapy (anticancer). This medicine can be hazardous to other animals and people that come in contact with it. On the day your animal gets the medicine, and then for a few days afterward, handle all bodily waste (ie, urine, feces, litter), blood, or vomit only while wearing disposable gloves.
- ■ Hydroxyurea can be toxic to the gastrointestinal tract, causing vomiting, diarrhea, ulcers, and stomach upset. Giving the medicine to your animal with food may decrease these side effects.
- ■ This medication is considered to be a hazardous drug as defined by the National Institute for Occupational Safety and Health (NIOSH). Talk with your veterinarian or pharmacist about the use of personal protective equipment when handling this medicine.
- Protect hydroxyurea capsules and tablets from light and store at 20°C to 25°C (68°F-77°F); keep bottle tightly closed.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Hydroxyurea is an oral antineoplastic (anti-cancer) agent primarily used in veterinary medicine to treat myeloproliferative disorders.
Key indications include:
- Polycythemia vera: Reduces excessive red blood cell production.
- Chronic myelogenous leukemia (CML): Often utilized when patients are no longer responsive to busulfan.
- Mast cell tumors (Mastocytomas).
- Cardiovascular shunts: Used adjunctively in right-to-left shunting patent ductus arteriosus (PDA) or Tetralogy of Fallot to reduce hematocrit and alleviate hyperviscosity.
- Feline hypereosinophilic syndrome and adjunctive treatment for canine meningiomas.
Clinical Pearl: Because it is a chemotherapy agent, strict handling precautions must be observed by both veterinary staff and pet owners to prevent accidental exposure.
Mechanism of action
Hydroxyurea is an S-phase specific antimetabolite.
- It specifically inhibits the enzyme ribonucleotide reductase → blocks the conversion of ribonucleotides to deoxyribonucleotides → halts DNA synthesis without significantly interfering with RNA or protein synthesis.
- Cells are arrested at the G1-S border.
- It also inhibits urease (though less potently than acetohydroxamic acid) and can stimulate the production of fetal hemoglobin.
Safety & warnings
Contraindications
- Pre-existing severe anemia or bone marrow depression
- History of urate stones
- Current severe infection
- Impaired renal function
- Patients who have recently received other chemotherapy or radiotherapy
- Pregnancy (proven teratogen)
Adverse effects
- Bone marrow depression (anemia, thrombocytopenia, leukopenia)
- GI effects (anorexia, vomiting, diarrhea)
- Stomatitis
- Sloughing of nails
- Alopecia
- Dysuria
- Pulmonary fibrosis
- Methemoglobinemia (especially in cats at high doses >500 mg)
Precautions
Warning: Hydroxyurea is a known teratogen and can suppress gonadal function (arrest of spermatogenesis noted in dogs). Use only during pregnancy when benefits outweigh risks. Nursing animals should receive milk replacer.
- Myelotoxicity: If bone marrow depression occurs, halt therapy until values return to normal.
- Feline Sensitivity: Cats are at higher risk for bone marrow toxicity and methemoglobinemia; monitor closely.
Drug interactions
May cause additive myelosuppression when used concurrently with hydroxyurea.
Hydroxyurea may raise serum uric acid levels; allopurinol may be required to control hyperuricemia.
Monitoring
- CBC with platelets at least every 1-2 weeks until stable; then every 3 months
- BUN/Serum Creatinine initially before starting treatment and then every 3-4 months
- Hematocrit levels (to guide tapering of dose)
Pharmacokinetics
Absorption
Well absorbed after oral administration.
Distribution
Crosses the blood-brain barrier.
Metabolism
About 50% of an absorbed dose is metabolized in the liver.
Elimination
Approximately 50% is excreted unchanged in the urine, and the hepatic metabolites are also excreted in the urine.
Overdose
Because of the potential toxicity of the drug, overdoses should be treated aggressively with gut emptying protocols employed when possible.
Cats given hydroxyurea in doses greater than 500 mg (total) may develop methemoglobinemia (characterized by cyanosis, respiratory distress, and dark-colored blood). Contact an animal poison control center for further guidance.
Available products
Formulations
- Oral capsules
- Oral suspension (compounded)
Human-labeled
- Hydroxyurea Oral Capsules: 200 mg, 300 mg, 400 mg & 500 mg (Hydrea, Droxia, generic)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Capsules should be stored in tight containers at room temperature. Avoid excessive heat. Compounded oral suspension (100 mg/mL in Syrpalta) retains >95% potency for 180 days at 25°C, but must be protected from light. Heating to 41°C results in an immediate 40% loss of drug potency.
Client information
CHEMOTHERAPY HANDLING PRECAUTIONS: This is an anti-cancer drug. Wear disposable gloves when handling the medication and when cleaning up your pet's urine, feces, or vomit. Pregnant women or individuals trying to conceive should not handle this medication.
- Administration: Give exactly as prescribed by your veterinarian. Do not open, crush, or split capsules unless specifically instructed to do so.
- Side Effects: Watch for loss of appetite, vomiting, or diarrhea. Contact your vet immediately if you notice unusual bleeding, bruising, lethargy, or signs of infection.
- Nail Changes: This medication may cause your pet's nails to become brittle or slough off.
- Cats: Cats are highly sensitive to this drug. Watch closely for breathing difficulties or blue/brown gums, which are medical emergencies.
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.