Chlorambucil in Cats
Veterinary Guide — Chlorambucil in Cats
1. Overview
Chlorambucil is an oral alkylating chemotherapeutic agent used in veterinary medicine off-label to treat certain cancers and immune-mediated diseases in cats. It is a derivative of nitrogen mustard and works by alkylating DNA, leading to impaired cell division and death of rapidly dividing cells (neoplastic and hyperactive immune cells). (PetMD)
2. Pharmacology
- Class: Alkylating agent (nitrogen mustard derivative). (PetMD)
- Mechanism: Forms covalent bonds with DNA, preventing replication and inducing apoptosis in malignant and overactive immune cells. (PetMD)
- Immunosuppressive: Also suppresses overactive immune responses in certain immune-mediated diseases. (PetMD)
3. Pharmacokinetics (Cats)
- Route: Oral administration. (PMC)
- Absorption: Rapid gastrointestinal absorption. (PMC)
- Peak Plasma Levels: ~170 ng/mL within ~15 minutes post-dose. (PMC)
- Half-Life: ~1.8 hours, indicating rapid clearance and little accumulation with appropriate dosing intervals. (PMC)
- Metabolism & Excretion: Metabolized and cleared rapidly; adjustments to dose frequency often influence overall exposure. (PMC)
4. Indications in Feline Patients
Chlorambucil may be used (often with prednisolone) for:
- Low-grade gastrointestinal lymphoma (small cell) with good response rates. (PMC)
- Chronic lymphocytic leukemia. (Vet eBooks)
- Localized nasal or nasopharyngeal lymphoma. (PubMed)
- Immune-mediated diseases like pemphigus complex or eosinophilic granuloma. (Vet eBooks)
5. Dosing in Cats
Chlorambucil is only available as 2 mg tablets. Dosing is individualized by body weight/condition and indication. Common regimens include daily, every other day (EOD), or pulsed (e.g., every 2 weeks) to balance efficacy and toxicity. (Vet eBooks)
Dosing Table (5 lb to 10 lb Cats)
| Weight | Approx mg/kg | Typical Dose (per cat) | Schedule | Notes |
|---|---|---|---|---|
| 5 lb (~2.3 kg) | ~0.5–0.9 | 1–2 mg | EOD or per protocol | Immune/low-grade lymphoma protocols common |
| 6 lb (~2.7 kg) | ~0.4–0.7 | 1–2 mg | EOD or per protocol | |
| 7 lb (~3.2 kg) | ~0.4–0.6 | 1–2 mg | EOD or per protocol | |
| 8 lb (~3.6 kg) | ~0.4–0.6 | 1–2 mg | EOD or per protocol | |
| 9 lb (~4.1 kg) | ~0.3–0.5 | 2 mg | EOD or per protocol | |
| 10 lb (~4.5 kg) | ~0.3–0.5 | 2 mg | EOD or per protocol | Often 2 mg every 48–72 h |
Typical schemes: ~20 mg/m² every 2 weeks for small cell GI lymphoma with prednisolone; 2 mg total dose every 48–72 h for immune disease. (Vet eBooks)
Note: Actual dosing should be determined by your veterinarian based on diagnosis, response, and side effects.
6. Side Effects
Common / Dose-Related
- Bone marrow suppression: leukopenia, thrombocytopenia, anemia — necessitates regular CBC monitoring. (PetMD)
- Gastrointestinal: vomiting, diarrhea, anorexia. (PetMD)
Less Common / Rare
- Neurological effects: myoclonus, tremors, seizures (rare but documented). (PubMed)
- Hepatotoxicity: rare but possible with long-term use. (Veterinary Help)
- Hair thinning: uncommon in cats. (PetMD)
7. Dosing Precautions
- Bone marrow disease: contraindicated. (Vca)
- Active infection: use with caution. (Vca)
- Pregnancy/lactation: avoid unless critical. (Vca)
- Concurrent myelosuppressive drugs: increase risk of toxicity. (Vca)
- Vaccinations: avoid live vaccines during treatment. (Vca)
- Handling precautions: chlorambucil is cytotoxic — gloves and careful disposal of waste recommended. (AURA Veterinary)
8. Monitoring
Routine CBCs and chemistry profiles are crucial:
- Before starting therapy
- Every 1–3 months or as advised
- More often if there’s clinical concern
Monitoring helps catch bone marrow suppression or organ dysfunction early. (Vca)
