Chlorambucil

BRAND NAMES

• Leukeran – the most widely recognized brand name for chlorambucil. 

• Clafen – used in some countries for the same active ingredient.

MECHANISM OF ACTION

Chlorambucil is an alkylating chemotherapy drug that works by attaching alkyl groups to DNA, causing cross-links between DNA strands. This prevents DNA replication and transcription, leading to cell-cycle arrest and apoptosis. It primarily targets rapidly dividing cancer cells, making it effective in treating chronic lymphocytic leukemia and certain lymphomas.

PHARMACOKINETICS

Absorption 

Chlorambucil is well absorbed orally, with peak plasma concentrations typically reached 1–2 hours after ingestion. Its oral bioavailability is high, and absorption is not significantly affected by food.

Distribution

Chlorambucil is widely distributed in the body, with a volume of distribution (Vd) of about 0.5–1 L/kg. It binds moderately to plasma proteins and penetrates tissues, including the liver and kidneys.

Metabolism

Chlorambucil is primarily metabolized in the liver by enzymatic conversion to phenylacetic acid mustard, an active metabolite, and other inactive compounds. This metabolism helps control the drug’s activity and facilitates excretion.

Excretion

Chlorambucil and its metabolites are mainly excreted through the urine, with a small amount eliminated in the feces. Renal clearance is the primary route, and both unchanged drug and metabolites are removed from the body over time.

PHARMACODYNAMICS

Chlorambucil works by alkylating DNA, causing cross-links that inhibit DNA replication and transcription. This leads to cell-cycle arrest and apoptosis, particularly in rapidly dividing cancer cells such as lymphocytes. Its cytotoxic effect slows disease progression in conditions like chronic lymphocytic leukemia and lymphomas.

ADMINISTRATION

Chlorambucil is administered orally as tablets, with dosing schedules tailored to the patient’s condition, body response, and blood counts. It is commonly given in short treatment cycles or continuous low-dose regimens under strict medical supervision, and the dose may be adjusted or temporarily stopped based on toxicity. Patients are advised to take it exactly as prescribed, with or without food, while undergoing regular blood tests to monitor safety and effectiveness.

DOSAGE AND STRENGTH

Chlorambucil is usually given orally. Typical adult dosing for chronic lymphocytic leukemia (CLL) starts at 0.1–0.2 mg/kg per day, often rounded to 2–6 mg daily, adjusted based on response and blood counts. For lymphomas, intermittent dosing (e.g., 6–10 mg/m² daily for 4–7 days every 4–6 weeks) may be used. The dose is carefully monitored to minimize bone marrow suppression, and treatment is adjusted according to hematologic and clinical response.

CONTRAINDICATIONS

Chlorambucil should not be used in patients with known hypersensitivity to the drug, severe bone marrow suppression, active infections, or pregnancy and breastfeeding due to the risk of fetal harm. Caution is also needed in patients with severe liver or kidney impairment.

DRUG INTERACTIONS

• Bone marrow–suppressing drugs (e.g., other chemotherapies, immunosuppressants) may increase the risk of cytopenias. 

• Allopurinol can reduce chlorambucil’s effectiveness by interfering with its metabolism. 

• Anticoagulants may require monitoring, as chlorambucil can affect clotting indirectly through bone marrow suppression. 

• Live vaccines should be avoided, as immunosuppression increases infection risk.

FOOD INTERACTIONS

Chlorambucil absorption is not significantly affected by food, so it can be taken with or without meals. However, patients should maintain consistent timing and follow medical advice to ensure proper dosing and monitoring.

SIDE EFFECTS

• Bone marrow suppression

• Nausea and vomiting

• Diarrhea

• Loss of appetite

• Elevated liver enzymes

• Rash

• Hair loss

OVER DOSE

• Severe bone marrow suppression (pancytopenia)

• Nausea and vomiting

• Diarrhea

• Mucositis

• antidote

TOXICITY

Chlorambucil can cause bone marrow suppression, nausea, vomiting, diarrhea, liver toxicity, rash, hair loss, fatigue, increased risk of infections, and rarely, secondary malignancies.