Vinblastine Sulfate — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	IV	2-3 mg/m²	Every 7 days	Duration: As part of chemotherapy protocol; typically 4-6 cycles Notes: Dose may be adjusted based on hematologic tolerance. Administer as slow IV bolus or infusion.
Cat	IV	1.5-2 mg/m²	Every 7 days	Duration: As part of chemotherapy protocol; typically 4-6 cycles Notes: Cats are more sensitive to neurotoxicity; use lower end of dose range.
Horse	IV	2-4 mg/m²	Every 7 days	Duration: As part of chemotherapy protocol Notes: For sarcoids, intralesional injection of 1-2 mg per lesion may be used.

Clinical Indications & Species Uses

General Indications

Antineoplastic agent for various tumors in companion animals

Dog (Canine)

Treatment of mast cell tumors
Treatment of lymphoma (as part of combination protocols)
Treatment of histiocytic sarcoma
Treatment of some carcinomas

Cat (Feline)

Treatment of lymphoma (as part of combination protocols)
Treatment of mast cell tumors

Horse (Equine)

Treatment of sarcoids (intralesional administration)
Treatment of lymphoma

Pharmacology & Mechanism of Action

Drug Class: Vinca Alkaloid | Pharmacological Group: Antineoplastic Agent

Mechanism of Action: Vinblastine binds to tubulin, inhibiting microtubule formation and disrupting mitotic spindle assembly. This arrests cell division in the M phase of the cell cycle, leading to cell death. It also interferes with other microtubule-dependent processes such as intracellular transport and cell motility.

Pharmacodynamics: Vinblastine is cell-cycle specific, acting primarily on cells in mitosis. It has potent cytotoxic activity against rapidly dividing cells, including neoplastic cells. It also has immunosuppressive properties and can affect normal tissues with high mitotic activity, such as bone marrow and gastrointestinal epithelium.

⚡ Pharmacokinetics Summary

Absorption: Vinblastine is not absorbed orally and must be administered intravenously. After IV administration, plasma concentrations decline rapidly due to extensive tissue distribution.

Distribution: Vinblastine is extensively distributed into tissues, with high concentrations in the liver, spleen, and lungs. It has a large volume of distribution. It crosses the blood-brain barrier poorly.

Metabolism: Vinblastine is primarily metabolized in the liver via the cytochrome P450 system, particularly CYP3A4, to active and inactive metabolites.

Excretion: Vinblastine is excreted primarily in bile and feces, with a smaller amount excreted in urine. Enterohepatic recirculation may occur.

Half-Life: Dog: terminal half-life approximately 13-20 hours; Cat: approximately 10-15 hours; Horse: approximately 5-10 hours.

Bioavailability: Oral bioavailability is negligible; must be administered intravenously.

Protein Binding: Moderately protein-bound (approximately 70-80%) in dogs and humans.

Available Formulations & Strengths

Injectable Solution 1 mg/mL (as sulfate) (IV)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to vinblastine or other vinca alkaloids
Severe bone marrow suppression (neutropenia, thrombocytopenia)
Active infection
Pregnancy (teratogenic)
Lactation (excreted in milk)

Warnings & Clinical Precautions:

Extreme care to avoid extravasation; severe tissue necrosis can occur
Hepatic impairment: reduce dose or avoid
Renal impairment: use with caution
Monitor complete blood count regularly
Use with caution in animals with pre-existing neurologic disease
Wear protective gloves when handling; cytotoxic agent
Do not administer intrathecally (fatal)

Adverse Effects & Reactions

Common:

Neutropenia (nadir at 4-7 days)
Gastrointestinal signs (vomiting, diarrhea, anorexia)
Mild lethargy

Serious / Severe:

Severe myelosuppression
Neurotoxicity (peripheral neuropathy, constipation, ileus)
Extravasation injury (tissue necrosis)
Anaphylaxis (rare)

Rare:

Hepatotoxicity
Cardiotoxicity
Alopecia (in some breeds)
Seizures (with high doses)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
CYP3A4 inhibitors (e.g., ketoconazole, itraconazole)	Increased vinblastine concentrations and toxicity	High
CYP3A4 inducers (e.g., phenobarbital, rifampin)	Decreased vinblastine efficacy	Moderate
Other myelosuppressive agents (e.g., doxorubicin, cyclophosphamide)	Additive bone marrow suppression	High
Phenytoin	Decreased phenytoin levels	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Severe neutropenia
Thrombocytopenia
Gastrointestinal ulceration
Neurotoxicity (seizures, ataxia)
Cardiovascular collapse

Emergency Treatment Protocol: There is no specific antidote. Treatment is supportive: hospitalization, IV fluids, broad-spectrum antibiotics for neutropenic fever, antiemetics, and gastrointestinal protectants. Consider granulocyte colony-stimulating factor (G-CSF) for severe neutropenia. Monitor vital signs and hematology closely.

Food Animal Withdrawal Times

Not approved for food animals; not to be used in animals intended for food production.

Storage, Handling & Regulatory Information

Storage Temperature: 2-8°C (refrigerate)

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light. Do not freeze. Store in original carton.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for human use; not specifically approved for veterinary use, but used extralabel in veterinary medicine.

Extra-Label (Off-Label) Use: In the US, extra-label use in food animals is prohibited. In companion animals, extra-label use is permitted under AMDUCA with appropriate veterinary oversight.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Vinblastine is a valuable chemotherapeutic agent in veterinary oncology, particularly for canine mast cell tumors and lymphoma. It is typically used in combination protocols. Due to its vesicant nature, meticulous IV administration is essential. Hematologic monitoring is critical to manage dose-limiting neutropenia. Premedication with antiemetics may be considered. Owners should be advised on handling and disposal of excreta. Prognosis depends on tumor type and stage.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)