Vincristine

Vincristine is a vinca alkaloid antineoplastic used in veterinary chemotherapy, particularly for lymphoid malignancies. It is a component of several multidrug protocols and has a major single-agent role in canine transmissible venereal tumor. A separate clinical application is adjunctive treatment of immune-mediated thrombocytopenia to accelerate platelet recovery.

Group

Vinca alkaloid antineoplastic

Mechanism of Action

Vincristine binds tubulin and disrupts microtubule assembly, preventing normal mitotic-spindle function and arresting dividing cells in metaphase. This produces cytotoxic activity against susceptible neoplastic cells. In thrombocytopenia, proposed effects include increased platelet release from megakaryocytes and reduced platelet clearance, although the precise contribution of individual mechanisms is incompletely defined.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Antitumor therapy	0.025–0.05 mg/kg	IV	Every 168 h	Weight-based alternative explicitly supplied; not an arithmetic conversion of body-surface dosing.
Body-surface antitumor therapy	Reference only	IV		0.5-0.75 mg/m2 IV once weekly as part of the specific chemotherapy protocol. Requires a body-surface-area dosing protocol.
Thrombocytopenia adjunct	0.02 mg/kg	IV	Every 168 h	Used with prednisolone; canine discussion describes prednisone 2 mg/kg without a full route/schedule here.
Thrombocytopenia single-dose adjunct	0.02 mg/kg	IV	Once	Generally a single treatment in this reference, distinct from the earlier weekly alternative.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Antitumor therapy	0.025–0.05 mg/kg	IV	Every 168 h	Weight-based alternative explicitly supplied; not an arithmetic conversion of body-surface dosing.
Body-surface antitumor therapy	Reference only	IV		0.5-0.75 mg/m2 IV once weekly as part of the specific chemotherapy protocol. Requires a body-surface-area dosing protocol.
Thrombocytopenia adjunct	0.02 mg/kg	IV	Every 168 h	Used with prednisolone; canine discussion describes prednisone 2 mg/kg without a full route/schedule here.

Indications

Combination chemotherapy for lymphoma and selected other lymphoid or hematopoietic malignancies in dogs and cats.
Treatment of canine transmissible venereal tumor.
Adjunctive treatment of canine immune-mediated thrombocytopenia to support more rapid platelet recovery alongside treatment of the immune-mediated process.

Contraindications

ABCB1-deficient dogs have increased toxicity risk.
Extravasation can cause severe injury.

Adverse effects

Constipation, peripheral neuropathy, tissue necrosis with extravasation and possible myelosuppression.

Toxicity

Overdose can be fatal, especially in cats, with marrow, neurologic and GI injury. Monitor CBC, cardiovascular status and ileus; no reliably effective antidote is established.

Preparations

Preparation	Form	Strength	Route
Vincristine sulfate injection 1 mg/mL	Injection	1 mg / mL	IV

Monitoring and Administration

Administer through a secure IV line and monitor CBC/platelets according to the oncology plan. Use cytotoxic handling precautions and avoid co-mixing other drugs.

A suspected extravasation requires immediate oncology-directed management.

Additional oncology protocols are expressed in body-surface units: dogs 0.5-0.75 mg/m2 every 1-2 weeks; cats every 1-3 weeks. Transmissible venereal tumor uses 0.5 mg/m2 IV weekly for 4-6 weeks, maximum 1 mg/dose. Immune thrombocytopenia also has 0.5-0.7 mg/m2 alternatives. These mg/m2 amounts are never copied numerically into mg/kg fields. Equine lymphoma combination schedules contain multiple agents and response-dependent maintenance intervals.

Vincristine is a vesicant. For suspected extravasation, stop administration and use an oncology-directed local management protocol; do not mix it with other medicines in the vial.