Vincristine Sulfate

Vinca Alkaloid Antineoplastic Agent

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IV 0.5-0.75 mg/m² (body surface area) or 0.02-0.025 mg/kg Once weekly Duration: As per chemotherapy protocol (e.g., CHOP protocol: 4-6 doses)
Notes: Administer as a slow IV bolus or infusion over 5-10 minutes. Extravasation is dangerous; ensure proper catheter placement.
Cat IV 0.5-0.75 mg/m² (body surface area) or 0.025 mg/kg Once weekly Duration: As per chemotherapy protocol
Notes: Cats are more sensitive to neurotoxicity; use lower end of dose range. Monitor for constipation and neurotoxicity.
Horse IV 0.01-0.02 mg/kg Once weekly Duration: As per protocol
Notes: Limited data; use with caution. May cause severe neurotoxicity.
Rabbit IV 0.5 mg/m² Once weekly Duration: As per protocol
Notes: Limited evidence; use with extreme caution.

Clinical Indications & Species Uses

General Indications
  • Treatment of various neoplasms, particularly hematopoietic tumors
  • Immune-mediated thrombocytopenia (off-label in dogs)
Dog (Canine)
  • Lymphoma (as part of combination chemotherapy protocols, e.g., CHOP)
  • Leukemia
  • Mast cell tumors (rescue therapy)
  • Transmissible venereal tumor (TVT)
  • Immune-mediated thrombocytopenia (IMT) (off-label use)
Cat (Feline)
  • Lymphoma (as part of combination chemotherapy protocols)
  • Leukemia
  • Mast cell tumors (rescue therapy)
Horse (Equine)
  • Equine sarcoid (intralesional or systemic use, though less common)
  • Lymphoma (rarely used)
Rabbit & Small Mammals
  • Lymphoma (limited reports, not standard)

Pharmacology & Mechanism of Action

Drug Class: Vinca Alkaloid | Pharmacological Group: Antineoplastic Agent

Mechanism of Action: Vincristine sulfate is a vinca alkaloid that binds to tubulin, inhibiting microtubule formation and disrupting mitotic spindle assembly. This leads to metaphase arrest in dividing cells, ultimately causing cell death. It is cell-cycle specific, acting primarily in the M phase. Additionally, it inhibits microtubule-dependent processes such as intracellular transport and secretion, which contributes to its cytotoxic effects.

Pharmacodynamics: Vincristine exhibits potent antitumor activity against a variety of neoplasms, particularly lymphomas and leukemias. It also has immunosuppressive properties and can cause thrombocytosis by stimulating megakaryocyte production. In veterinary medicine, it is used for its cytotoxic effects and to treat immune-mediated thrombocytopenia (IMT) by promoting platelet release. The drug's efficacy is dose-dependent and schedule-dependent, with multiple doses often required for optimal response.

⚡ Pharmacokinetics Summary

Absorption: Vincristine is not absorbed orally and must be administered intravenously. Following IV administration, peak plasma concentrations are achieved rapidly.
Distribution: Vincristine is extensively distributed to tissues, with high concentrations in the liver, spleen, and kidneys. It has a large volume of distribution and crosses the blood-brain barrier poorly. Protein binding is approximately 75% in humans, but may vary in animals.
Metabolism: Vincristine undergoes extensive hepatic metabolism primarily via the cytochrome P450 enzyme system (CYP3A4 in humans). Metabolites are less active than the parent compound.
Excretion: The drug is primarily excreted in bile and feces, with only about 10-20% excreted renally. Enterohepatic recirculation may occur. Clearance is hepatic-dependent, and dose adjustments may be necessary in patients with hepatic impairment.
Half-Life: Dogs: approximately 1-2 hours (terminal half-life); Cats: approximately 1-3 hours; Horses: approximately 1-2 hours.
Bioavailability: Oral bioavailability is negligible; therefore, only IV administration is recommended.
Protein Binding: Approximately 75% in humans; may vary in animals.

Available Formulations & Strengths

Injectable Solution 1 mg/mL (single-use vials) (IV)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to vincristine or other vinca alkaloids
  • Severe hepatic impairment (dose reduction may be necessary)
  • Pregnancy (teratogenic)
  • Lactation (may be excreted in milk)
  • Concurrent use with radiation therapy (may increase toxicity)
Warnings & Clinical Precautions:
  • Extravasation hazard: causes severe tissue necrosis; administer via secure IV catheter.
  • Immunosuppression: monitor for infections.
  • Neurotoxicity: especially in cats; monitor for constipation, ileus, and peripheral neuropathy.
  • Hepatic function: monitor liver enzymes; adjust dose if impaired.
  • Use with caution in debilitated or geriatric patients.
  • Wear protective gloves when handling; avoid skin contact.
  • Do not administer intrathecally (fatal).

Adverse Effects & Reactions

Common:

  • Constipation
  • Ileus
  • Mild myelosuppression (less than other chemotherapeutics)
  • Alopecia (in some breeds)
  • Nausea/vomiting (less common)

Serious / Severe:

  • Severe neurotoxicity (peripheral neuropathy, paralytic ileus)
  • Extravasation necrosis
  • Severe immunosuppression (rare)
  • Hepatotoxicity (rare)

Rare:

  • Cardiotoxicity
  • Seizures
  • Anaphylaxis

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Asparaginase May increase neurotoxicity; administer asparaginase before vincristine to reduce risk. Moderate
Phenytoin Decreases phenytoin levels; monitor anticonvulsant levels. Moderate
CYP3A4 inhibitors (e.g., ketoconazole, itraconazole) May increase vincristine toxicity by reducing metabolism. High
CYP3A4 inducers (e.g., phenobarbital) May decrease vincristine efficacy by increasing metabolism. Moderate
Mitomycin C Increased risk of respiratory toxicity. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe neurotoxicity (seizures, ataxia, paralysis)
  • Bone marrow suppression (pancytopenia)
  • Gastrointestinal signs (vomiting, diarrhea, ileus)
  • Tissue necrosis at injection site (if extravasation)

Emergency Treatment Protocol: There is no specific antidote. Treatment is supportive: hospitalization, IV fluids, antiemetics, laxatives for constipation, and monitoring of neurologic and hematologic parameters. In severe cases, granulocyte colony-stimulating factor (G-CSF) may be considered for neutropenia. Extravasation should be treated immediately with local infiltration of hyaluronidase and warm compresses.

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 widely used in veterinary oncology.

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 veterinary discretion. Follow AMDUCA guidelines.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Vincristine is a cornerstone of many veterinary chemotherapy protocols, particularly for lymphoma in dogs and cats. It is also used off-label for immune-mediated thrombocytopenia in dogs. Due to its vesicant nature, meticulous IV administration is essential. Dose adjustments are required in hepatic insufficiency. Cats are particularly prone to neurotoxicity, so monitor for constipation and ileus. Always wear protective equipment when handling. Prognosis depends on the underlying condition and response to therapy.

References & Literature

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