Cytarabine
Cytosine arabinoside
Also known as: Cytosar-U · DepoCyt · Tarabine PFS · Ara-C · 1-beta-D-arabinofuranosylcytosine · arabinosylcytosine · cytarabine liposome · cytarabinum · NSC-63878 · U-19920
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
This dose is based on body surface area (mg/m²). Convert body weight to body surface area before dosing.
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 |
|---|---|---|---|---|---|
| Susceptible neoplastic diseases | 100 mg/m2 | IV/SC | continuous infusion over 2-3 days or divided and given IV or SC for 2-4 days | 2-4 days | 🌎 NA |
- Susceptible neoplastic diseases: Dosed in mg/m2 (NOT mg/kg). Use only as a general guide.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible neoplastic diseases | 100 mg/m2 | IV/SC | continuous infusion over 2-3 days or divided and given IV or SC for 2-4 days | 2-4 days | 🌎 NA |
- Susceptible neoplastic diseases: Dosed in mg/m2 (NOT mg/kg). Cats are generally dosed similarly to dogs.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Neoplastic diseases | 200-300 mg/m2 (usually 1-1.5 grams per horse per dose) | SC/IM/IV | every 1-2 weeks | — | 🌎 NA |
- Neoplastic diseases: Consultation with a veterinary oncologist is encouraged before use.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Cytarabine (often referred to as Ara-C) is a synthetic pyrimidine nucleoside antimetabolite primarily used in veterinary medicine for the treatment of lymphoreticular neoplasms, myeloproliferative diseases (leukemias), and CNS lymphoma in dogs and cats.
Clinical Pearl: Beyond traditional oncology, cytarabine is widely utilized in veterinary neurology as a cornerstone immunosuppressive therapy for Meningoencephalitis of Unknown Etiology (MUE) and Granulomatous Meningoencephalomyelitis (GME) in dogs. Its ability to cross the blood-brain barrier, especially when administered as a continuous rate infusion (CRI) or via high-dose subcutaneous protocols, makes it highly effective for CNS inflammatory diseases.
Mechanism of action
Cytarabine is a cell-cycle phase-specific antimetabolite that acts principally during the S-phase (active DNA synthesis).
- Intracellular Conversion: Cytarabine enters the cell and is phosphorylated into its active form, cytarabine triphosphate.
- Enzyme Inhibition: This active metabolite competes with deoxycytidine triphosphate → incorporates into DNA → potently inhibits DNA polymerase.
- Result: Inhibition of DNA synthesis and repair, leading to cell death in rapidly dividing cells. Under certain conditions, it may also block cells from transitioning from the G1 phase to the S phase.
Safety & warnings
Contraindications
- Hypersensitivity to cytarabine
- Pregnancy (potentially teratogenic and embryotoxic)
Adverse effects
- Myelosuppression (leukopenia, anemia, thrombocytopenia)
- Anorexia
- Nausea
- Vomiting
- Diarrhea
- Conjunctivitis
- Oral ulceration
- Neurotoxicity
- Hepatotoxicity
- Fever
- Anaphylaxis (rare)
Precautions
Cytarabine is a mutagenic and potentially carcinogenic agent. It should only be used in patients who can be adequately and regularly monitored. Personnel preparing or administering the drug must wear gloves and follow hazardous drug handling protocols. Wash skin or mucous membranes thoroughly if contamination occurs.
Drug interactions
Cytarabine may decrease the amount of digoxin (tablets only) absorbed after oral dosing due to intestinal mucosa alterations; effect may persist for several days after cytarabine discontinuation.
Cytarabine may antagonize the anti-infective activity of flucytosine; monitor for decreased efficacy.
Cytarabine may antagonize the anti-infective activity of gentamicin; monitor for decreased efficacy.
Monitoring
- Efficacy (tumor response or resolution of neurologic signs)
- Hemograms (mandatory; monitor for myelosuppression, nadir typically at 5-7 days)
- Liver function tests (periodic)
- Kidney function tests (periodic)
Pharmacokinetics
Absorption
Very poor systemic availability after oral administration. Following IM or SC injections, peaks in plasma within 20-60 minutes, but levels are much lower than equivalent IV doses.
Distribution
Widely distributed throughout the body. Crosses into the CNS in a limited manner with bolus injection, but continuous IV infusion achieves CSF levels 20-60% of plasma levels. About 13% bound to plasma proteins in humans. Crosses the placenta.
Metabolism
Rapidly metabolized by the enzyme cytidine deaminase (principally in the liver, but also kidneys, intestinal mucosa, and granulocytes) to the inactive metabolite ara-U (uracil arabinoside).
Elimination
About 80% of a dose is excreted in the urine within 24 hours as both ara-U (≈90%) and unchanged cytarabine (≈10%). Elimination half-life in the CSF is significantly longer than in serum.
Overdose
Efficacy and toxicity are dependent on both the dose and the rate of administration. In dogs, the IV LD50 is 384 mg/kg when given over 12 hours, but drops to 48 mg/kg when infused IV over 120 hours. In the event of an inadvertent overdose, aggressive supportive therapy should be instituted.
Available products
Formulations
- Powder for injection
- Injection solution
- Liposomal injection
Human-labeled
- Cytarabine Powder for Injection: 100 mg, 500 mg, 1 g & 2 g in vials
- Cytarabine Injection: 10 mg/mL (liposomal) preservative free in 5 mL vials
- Cytarabine Injection: 20 mg/mL in 5 mL vials & 50 mL bulk package vials
- Cytarabine Injection: 100 mg/mL in 20 mL single-dose vials
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store sterile powder at room temperature (15-30°C). After reconstitution with bacteriostatic water, solutions are stable for at least 48 hours at room temperature (some studies show 90% potency retention up to 17 days). Discard if the solution develops a slight haze.
Client information
Cytarabine is a potent chemotherapy drug.
- Toxicity Risks: Be aware of the potential for severe toxicity, including life-threatening complications or drug-related mortality.
- When to Call the Vet: Contact your veterinarian immediately if your pet exhibits profound depression, lethargy, abnormal bleeding (e.g., bleeding gums, nosebleeds), bruising, fever, or severe gastrointestinal upset.
- Safe Handling: Because this is a hazardous drug, follow your veterinarian's instructions regarding the safe handling of your pet's waste (urine/feces) for a few days following treatment.
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.