Leustatin (Cladribine)

Leustatin (cladribine) is indicated for diseases where abnormal lymphocyte proliferation is a key pathogenic factor.

• Relapsing multiple sclerosis: reduces annual relapse rate, decreases new lesion formation on MRI, and slows disability progression by selectively depleting pathogenic B and T lymphocytes.
• Hairy cell leukemia: induces durable remission by targeting malignant B‑cell clones, causing DNA strand breaks and apoptosis of the leukemic cells, leading to hematologic recovery.

• Cladribine is a purine nucleoside analog that is taken up by proliferating lymphocytes via nucleoside transporters. Inside the cell it is phosphorylated to the active triphosphate form, which is incorporated into DNA in place of deoxyadenosine. This incorporation triggers DNA strand breaks, inhibits repair enzymes, and ultimately leads to apoptosis of the targeted lymphocyte population, reducing abnormal immune activity and modulates cytokine release.

Cladribine may be associated with a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Fatigue: persistent tiredness that may limit activity.
• Nausea: mild to moderate upset stomach.
• Headache: transient cranial discomfort.
• Fever: low-grade temperature rise.
• Lymphopenia: reduced lymphocyte count without infection.
• Transient liver enzyme elevation: temporary increase in ALT/AST.

Serious or Rare Side Effects

• Severe infections: opportunistic or serious bacterial infections.
• Secondary malignancies: emergence of new cancers.
• Profound lymphopenia with immunosuppression: marked reduction in immune cells.
• Hepatic toxicity: significant liver injury or failure.
• Autoimmune disorders: new onset thyroiditis or other autoimmune disease.

When using Leustatin, clinicians should observe several safety precautions to minimize risk.

• Monitor blood counts: perform regular CBC to detect lymphopenia.
• Assess infection risk: screen for active infections before initiation.
• Evaluate liver function: check ALT/AST levels periodically.
• Contraindicated in severe immunosuppression: avoid in patients with profound immune deficiency.
• Pregnancy and lactation: use only if benefits outweigh unknown risks.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Cladribine can interact with other medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Live vaccines: increased risk of vaccine‑derived infection.
• Concurrent immunosuppressants: additive immunosuppression may cause severe infections.
• Antiviral nucleoside analogs: competitive inhibition may reduce cladribine activation.

Moderate Interactions (Monitor Closely)

• CYP450 substrates: cladribine may affect metabolism of drugs processed by CYP enzymes.
• Non‑live vaccines: timing may need adjustment to ensure adequate immune response.
• Renal‑clearing drugs: monitor dosing in patients with impaired kidney function.