🐾💊 Chlorambucil for Dogs and Cats: Vet-Approved Cancer and Immune Therapy Guide 2025

By Dr Duncan Houston BVSc

When it comes to treating cancer or certain immune-mediated diseases in dogs and cats, one medication that frequently stands out is Chlorambucil, sold under the brand name Leukeran®. This powerful yet slow-acting chemotherapy drug offers hope in managing non-localized cancers and persistent autoimmune conditions. 🧬🐕🐈

In this comprehensive 2025 veterinary guide, we’ll cover everything pet parents need to know about Chlorambucil—from how it works, what it treats, possible side effects, drug interactions, and how to handle pets undergoing this form of chemotherapy. 📘💊

🔬 What Is Chlorambucil?

Chlorambucil is a chemotherapy drug known as an alkylating agent—a class of medications that binds directly to DNA, interfering with cell division. This makes it especially useful against cancers that spread through the body and immune disorders where rapidly dividing immune cells need to be suppressed. ⚙️🧪

📍 How It Works

Chlorambucil prevents DNA from unzipping—an essential step in cell division. This disrupts replication in fast-dividing cells, such as cancer cells and hyperactive immune cells. Because it acts more slowly than many chemotherapy drugs, it tends to cause fewer side effects—particularly in cats. 🐈🧬

💡 When Is Chlorambucil Used?

Veterinarians use Chlorambucil in two major medical areas:

🎗️ Cancer Treatment

• Lymphocytic leukemia
• Lymphoma (especially small-cell intestinal lymphoma in cats)
• Ovarian cancer
• Multiple myeloma
• Polycythemia rubra vera

🛡️ Immune-Mediated Diseases

• Inflammatory bowel disease (IBD)
• Pemphigus complex (autoimmune skin disease)
• Eosinophilic granuloma complex (especially in cats)
• Immune-mediated hemolytic anemia (IMHA)
• Immune-mediated thrombocytopenia (IMTP or ITP)

Because of its versatility, Chlorambucil is often a second-line treatment when corticosteroids alone are insufficient. 💊

📅 Dosage & Administration

Chlorambucil is available in 2 mg tablets and may be prescribed:

• Daily
• Every other day
• Every third day
• In pulsed high doses every few weeks (less common)

Results can take 2–4 weeks to become noticeable, so patience is key. If a dose is missed, wait the appropriate time before giving the next dose—never double up. 📆⏳

Administer on an empty stomach unless your pet experiences nausea. Always handle tablets carefully—do not crush or split. 🧤💊

⚠️ Side Effects

Chlorambucil is generally well-tolerated but has the potential for serious side effects, especially at higher or prolonged doses:

🩸 Bone Marrow Suppression

This is the most significant risk. Bone marrow is where new blood cells are made. Suppression can lead to:

• Anemia – not enough red cells
• – not enough white cells (weakened immune response)
• Thrombocytopenia – low platelets (bleeding issues)

These issues usually appear in the second week of treatment. Your vet will run blood tests to monitor your pet’s cell counts. 🩺🧪

🐩 Hair Loss in Certain Breeds

• More common in breeds like Poodles or Kerry Blue Terriers
• Widespread fur loss like humans on chemo is rare in pets

⚡ Neurological Symptoms (Rare)

Overdose or sensitivity may cause seizures or muscle twitching. If this occurs, discontinue immediately and call your vet. 🧠🚨

💊 Drug Interactions

Because Chlorambucil affects the bone marrow, combining it with other marrow-suppressing medications increases risk. Avoid concurrent use with:

• Chloramphenicol
• Azathioprine
• Colchicine
• Cyclophosphamide

It may also require an increased dose of allopurinol in dogs with uric acid bladder stones (e.g., Dalmatians). 🧬💊

🧤 Safe Handling Tips

Since Chlorambucil is a chemotherapy drug, it can be present in your pet’s urine and feces for up to a week after dosing. Proper cleanup is crucial:

• Use gloves to handle urine, feces, or vomit 🧤
• Clean accidents with dilute bleach solution
• Double-bag waste (litter, paper towels) and discard in trash 🗑️
• Keep pets away from public or child-accessible areas for 72 hours
• Litter boxes should be cleaned daily 🐈
• Soiled linens should be washed separately 🧺
• Pregnant women should avoid contact with pet waste during treatment 🤰

🚫 Cautions and Contraindications

• Never use in pregnant animals
• Avoid in pets with pre-existing bone marrow issues
• Use cautiously in immunocompromised pets (e.g., FIV+ cats)
• May cause permanent infertility if given before sexual maturity

📞 When to Contact Your Vet

Call your veterinarian immediately if you notice:

• Weakness, pale gums (signs of anemia)
• Frequent infections or fevers
• Bleeding or bruising
• Seizures or twitching
• Appetite loss or vomiting

📲 Support at Your Fingertips with Ask A Vet

Worried about side effects or how to safely clean up after your pet on Chlorambucil? Download the Ask A Vet app to chat with licensed veterinarians any time, anywhere. 🐾💬

From cancer care to chronic disease support, Ask A Vet is your trusted partner in pet health. 📱🐕🐈

✅ Final Thoughts

Chlorambucil is a life-changing medication for pets battling systemic cancers or immune disorders. When administered properly and monitored closely, it offers a targeted and relatively gentle approach to long-term disease control. 🧬💖

Always follow your vet’s dosing instructions, handle with care, and never hesitate to reach out for guidance. With proper use, Chlorambucil can offer comfort, control, and quality of life to pets facing serious conditions. 🐾🎗️

– Dr Duncan Houston BVSc

💡Need help navigating pet cancer or autoimmune conditions? Visit AskAVet.com or download the Ask A Vet app to talk with expert veterinarians today!