Vinblastine

Overview

Vinblastine (Velban®) is a vinca alkaloid antineoplastic agent used in dogs and cats for the treatment of a variety of neoplastic diseases. It is commonly incorporated into chemotherapy protocols for selected solid tumors and lymphoproliferative disorders and is often administered in combination with other anticancer medications.

In veterinary oncology, vinblastine is used less frequently than vincristine for lymphoid malignancies but remains an important component of treatment protocols for canine mast cell tumors and certain urinary bladder tumors. Because the drug can cause significant bone marrow suppression, careful patient monitoring and dose adjustments are often required during therapy.

Vinblastine is administered intravenously and is a local tissue irritant; therefore, it should be given through a properly placed intravenous catheter to minimize the risk of extravasation injury. Patients with hepatic dysfunction may require dose reductions because drug metabolism can be impaired.

Mechanism of Action (MOA): Vinblastine binds to tubulin and disrupts microtubule formation within dividing cells. This inhibits mitotic spindle assembly, arrests cell division during mitosis, and ultimately leads to death of rapidly proliferating neoplastic cells.

Indications

Vinblastine is used in dogs and cats as part of chemotherapy protocols for selected neoplastic diseases.

• Mast cell tumors: Commonly used in combination with prednisolone for the treatment of canine mast cell tumors.
• Lymphoproliferative disorders: May be used as part of chemotherapy protocols for certain lymphoid malignancies.
• Transitional cell carcinoma: Used in the management of urinary bladder transitional cell carcinoma.

Dosage (Reference)

Dog

Vinblastine dosing varies according to the chemotherapy protocol and tumor type being treated. The drug is administered intravenously and doses are calculated using body surface area (BSA), not body weight.

Cat

In cats, vinblastine dosing is protocol-dependent and calculated using body surface area rather than body weight. Treatment intervals are determined by the specific cancer type and chemotherapy regimen.

Warnings & Precautions

Vinblastine is a cytotoxic chemotherapeutic agent with significant hematologic and neurologic toxicity potential. Careful patient selection, dose adjustment, and monitoring are essential throughout treatment.

• Bone marrow suppression: Contraindicated in patients with pre-existing leukopenia, granulocytopenia, or significant bone marrow suppression unless these abnormalities are a consequence of the disease being treated.
• Active infections: Avoid use in patients with active bacterial infections because treatment-related myelosuppression may impair the ability to control infection.
• Hepatic dysfunction: Reduce vinblastine dose. In humans, a 50% reduction in dose is recommended when transaminases (AST/ALT) are 2 to 3 times the upper limit of normal — useful as a starting reference in dogs and cats with comparable enzyme elevations.
• MDR1 mutation: Susceptible breeds include Collies, Australian shepherds, Shetland sheepdogs, long-haired whippets, and “white feet” herding breeds. Test before treatment if available; for mutant/normal or mutant/mutant dogs, reduce dose by 25-30% (WSU recommendation).
• Extravasation risk: Vinblastine is a vesicant — administer through a properly placed IV catheter. If extravasation occurs: stop infusion immediately, apply moderate (dry) heat to disperse the drug, consider local hyaluronidase. DO NOT use ice — it has been shown to significantly increase skin ulceration with vinca alkaloid extravasation.
• Cats: Feline patients may be particularly susceptible to neurotoxicity, including constipation, hyporexia, and paralytic ileus.
• Hazardous drug handling: Appropriate chemotherapy safety precautions should be followed during preparation and administration, including the use of protective gloves and clothing.
• Reproductive risk: Vinblastine is teratogenic and embryotoxic in laboratory animals and may also cause aspermia in males. Verify pregnancy status before dosing in sexually intact females. Excretion in milk is unknown — use milk replacer if the dam requires vinblastine.
• IV use ONLY: Vinblastine is for intravenous administration only and may be FATAL if given by any other route
• Tall-man lettering: Always write vinBLAStine vs vinCRIStine with tall-man capitalisation on prescriptions to reduce dispensing errors.
• Do NOT use for platelet support: Do NOT use vinblastine to increase platelet numbers (as is sometimes done with vincristine). Vinblastine may actually cause thrombocytopenia.
• Client waste handling: For at least 3 days after each dose, handle all bodily waste (urine, faeces, litter, blood, vomit) only while wearing chemotherapy-resistant gloves. Seal the waste and gloves in a plastic bag and discard with regular trash. Do NOT wash items soiled with waste or vomit with other laundry. Pregnant, conceiving, or nursing household members should not clean up the animal’s waste.

Drug Interactions

• CYP P450 inhibitors: Any drugs that inhibit metabolism via hepatic cytochrome P450 system may reduce metabolism and thus increase toxicity of vinblastine, e.g. calcium-channel blockers, cimetidine, ciclosporin, erythromycin, metoclopramide and itraconazole.
• P-glycoprotein inhibitors: Drugs that are inhibitors of P-glycoprotein (ciclosporin, verapamil, phenothiazines and itraconazole) may increase the toxicity.
• Macrolide antibiotics (except azithromycin): Erythromycin and clarithromycin may increase vinblastine serum concentrations. Azithromycin is the macrolide exception .
• Ototoxic drugs: Ototoxic drugs (e.g., cisplatin, carboplatin): Concurrent use may cause additive risk for ototoxicity.
• Immunosuppressive drugs: Immunosuppressive drugs (e.g., azathioprine, cyclophosphamide, corticosteroids): Concurrent use may increase the risk of infection. Monitor and counsel owners accordingly.
• Myelosuppressive agents: Other antineoplastics, immunosuppressants, and iron chelators may produce additive myelosuppression; avoid combinations where possible.
• Vaccines (live and inactivated): Vinblastine may diminish vaccine efficacy and enhance adverse effects of vaccines. Avoid vaccination during chemotherapy and for a period after, per oncology guidance.
• Other P-glycoprotein inhibitors: Amiodarone, Azole antifungals (ketoconazole, itraconazole), Carvedilol, Cyclosporine, Diltiazem, Erythromycin/Clarithromycin, Quinidine, Spironolactone, Tamoxifen, Verapamil may all increase intracellular vinblastine and toxicity, particularly in MDR1 mutant or MDR1-untested dogs of susceptible breeds.

Side Effects & Overdose

Side Effects

The principal dose-limiting toxicity of vinblastine is myelosuppression. Gastrointestinal and neurologic adverse effects may also occur, particularly with repeated treatment or higher cumulative exposure.

• Myelosuppression: The most important adverse effect — typically neutropenia. Nadir occurs about 1 week after administration with recovery at 2 weeks.
• Gastrointestinal toxicity: Nausea, vomiting, mucositis, stomatitis, and other gastrointestinal disturbances may occur.
• Constipation and ileus: Reduced gastrointestinal motility may develop, ranging from mild constipation to ileus.
• Neurotoxicity: At high doses, vinblastine may cause peripheral neurotoxic effects similar to those seen with vincristine. also may cause jaw and muscle pain, and loss of deep tendon reflexes
• Cats: Constipation, hyporexia, and paralytic ileus. Cats can also develop reversible axon swelling and paranodal demyelination . These cat-specific findings are part of the rationale for substituting vinblastine for vincristine in some feline protocols (lower GI toxicity) while still monitoring for neurotoxicity.
• Alopecia: Hair loss may occur during treatment.
• Inappropriate ADH secretion: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) has been reported.
• Injection-site injury: Vinblastine is a vesicant — perivascular leakage causes significant tissue irritation and cellulitis.

Overdose

Overdose is expected to produce exaggerated manifestations of the drug’s known toxicities, particularly severe bone marrow suppression, gastrointestinal injury, and neurologic adverse effects.

• Severe myelosuppression: Marked neutropenia, leukopenia, and increased susceptibility to secondary infections may occur.
• Severe gastrointestinal toxicity: Pronounced mucositis, stomatitis, vomiting, constipation, or ileus may develop.
• Neurologic toxicity: Exaggerated neurotoxic effects, including muscle pain, loss of reflexes, and severe gastrointestinal hypomotility, may occur.
• Cats: Feline patients may be at increased risk of severe neurotoxicity and paralytic ileus.
• Management: Manage with anticonvulsants if seizures, ileus prophylaxis (prokinetics), and SIADH management (fluid restriction + loop diuretics to maintain serum osmolality). Consult a 24-hour veterinary poison consultation centre for any suspected or confirmed overdose.

Key Notes

Practical clinical points that help optimize the use of vinblastine in dogs and cats undergoing cancer treatment:

• Less commonly used than vincristine: Vinblastine is generally used less frequently than vincristine for lymphoproliferative disorders but remains an important drug in selected oncology protocols.
• Important role in mast cell tumor protocols: Vinblastine is a cornerstone drug in many treatment protocols for canine mast cell tumors, often combined with prednisolone and other chemotherapeutic agents.
• Body surface area dosing: Doses are calculated using body surface area (mg/m²) rather than body weight, which is standard practice for many chemotherapy drugs.
• Protocol-dependent use: Treatment schedules vary considerably depending on tumor type, disease stage, and the overall chemotherapy protocol being followed.
• Combination chemotherapy: Vinblastine is commonly incorporated into multidrug protocols rather than being used as a sole antineoplastic agent.
• Potential benefit of higher doses in mast cell tumors: Limited clinical evidence suggests that 3 mg/m² may provide lower recurrence rates than 2 mg/m² in some dogs with mast cell tumors.
• Oncology specialist involvement: Treatment planning, dose adjustments, and monitoring are ideally performed in consultation with a veterinarian experienced in cancer chemotherapy.
• No cross-resistance with vincristine: There does not appear to be cross-resistance from vincristine to vinblastine . Vinblastine may therefore be considered when a vincristine-containing protocol has failed.
• Cat lymphoma substitution: In feline COP-based protocols, vinblastine has similar efficacy but less GI toxicity than vincristine — common rationale for substituting vinblastine for vincristine in cats.