Chlorambucil

Chlorambucil is a chemotherapy drug. It belongs to the alkylating agents and slows down cell division, including that of immune cells. In dogs, the vet uses it for certain slow-growing cancers of the blood and lymph nodes, and as a medicine that dampens an overactive immune system.

Important: Chlorambucil can suppress blood cell production in the bone marrow. Your dog then has fewer immune cells and fewer platelets. If he has a fever, suddenly seems listless, does not eat, or has bloody diarrhoea, bleeding or bruises, call your veterinary practice straight away.

We are not aware of any veterinary medicine containing chlorambucil in Switzerland, Germany and Austria (as of October 2026). If no authorised veterinary medicine is available, the vet may switch to another medicine in individual cases. A fixed order applies to this, and a product for humans is the last option. This is called off-label use (known as cascade use in Europe), and it is reserved for vets.

How does chlorambucil work?

Chlorambucil binds to the genetic material (DNA) of cells and cross-links it so that the cell can no longer divide properly. The body does not first need to convert the substance in the liver for this. Compared with other drugs in this group, chlorambucil is considered slow-acting. This is why it is mainly used for diseases that progress slowly.

Uses of chlorambucil in dogs

Chronic lymphocytic leukaemia: a slowly progressing blood cancer in which certain white blood cells multiply.

Small cell lymphoma: a slow-growing form of lymph node cancer.

Mast cell tumours: together with prednisolone, when the tumour cannot be operated on.

Metronomic chemotherapy: Here the dog receives a low dose regularly over a longer period, which is meant to slow tumour growth.

Immune-mediated diseases: as a second-choice medicine when cortisone alone is not enough or is not tolerated. One example is a chronic bowel disease in which the dog loses a lot of protein. There, chlorambucil is combined with prednisolone.

Administration and dosage

Chlorambucil is given by mouth as a tablet. The dose and schedule are always set by the vet, depending on the disease, weight and blood values. Give it only as instructed, and do not stop or change it on your own. If you have missed a dose, ask the practice rather than giving double the amount.

Handling at home: Chlorambucil is a cytotoxic substance, for humans too. Do not split or crush the tablets. When giving them, wear the gloves you receive from the practice, and wash your hands afterwards. Also clear up urine, faeces and vomit with disposable gloves for at least three days after a dose; ask the practice exactly how long. During this time, let your dog relieve himself outdoors, if possible in a spot where few people spend time. Anyone who is pregnant, wants to become pregnant or is breastfeeding should not give the tablets or clear up waste. Store the tablets separately from your own medicines and out of the reach of children.

Side effects of chlorambucil

• Blood count: The bone marrow produces fewer blood cells. The platelets in particular can gradually decrease with longer use. This raises the risk of infections and the tendency to bleed.
• Digestion: nausea, vomiting, diarrhoea, reduced appetite.
• Nervous system: Seizures have been described in isolated cases.

Watch out for: If your dog has a seizure, bleeds from the nose or gums, has blood in his faeces or urine, or has small red dots on his skin, contact the veterinary practice straight away.

Monitoring during treatment

During treatment, the vet regularly checks the blood count, meaning red and white blood cells and platelets. If the values drop too far, the vet adjusts or pauses the treatment. Keep the check-up appointments even when your dog is doing well.

Because the immune defences can be weakened, a fever or any sign of infection during treatment is always a reason to call the practice straight away.

When is caution needed?

If your dog already has few blood cells before treatment or currently has an infection, the vet weighs things up particularly carefully, because chlorambucil can further suppress blood cell production. If your bitch is pregnant or nursing, the vet decides whether treatment is an option.

So tell the vet which other medicines your dog receives, especially other cancer drugs or medicines that dampen the immune system, whether he currently has an infection and whether your bitch is pregnant or nursing.

Conclusion

Chlorambucil is a chemotherapy drug that is used in dogs mainly for slow-growing cancers and for immune-mediated diseases. We are not aware of any authorised veterinary medicine in Switzerland, Germany and Austria; the vet uses it off-label. Regular blood checks and careful handling of tablets and waste are part of the treatment.