Ibritumomab

• Class: Monoclonal antibody – anti-CD20 radioimmunotherapy.
• Type: Murine IgG1 mAb conjugated to yttrium-90 or indium-111.

Mechanism of Action (MOA)

• Targets CD20 on B-cells → delivers radiation directly to malignant B-cells.
• Dual action:
  1. Antibody-dependent B-cell targeting.
  2. Localized beta-particle radiation → cytotoxicity to targeted and nearby malignant cells (“cross-fire effect”).
• Induces apoptosis and DNA damage in tumor cells.

Clinical Uses

• Relapsed or refractory low-grade or follicular B-cell non-Hodgkin lymphoma.
• Can be used:
  • After rituximab-containing regimens.
  • As consolidation after first remission in selected patients.

Dosing

• Two-step process:
  1. Indium-111 labeled imaging dose – confirms biodistribution.
  2. Yttrium-90 therapeutic dose – single IV infusion.
• Dose based on body weight or body surface area and platelet count.

Toxicities

• Hematologic toxicity – dose-limiting:
  • Neutropenia, thrombocytopenia, anemia (nadir ~4–6 weeks).
  • Recovery ~8 weeks.
• Infusion reactions (mild/moderate).
• Rare: myelodysplastic syndrome or secondary AML.
• Infection risk due to prolonged cytopenias.
• Radiation precautions: transient isolation not typically required, but follow institutional protocols.

Monitoring

• CBC weekly for at least 8 weeks post-infusion.
• Monitor for infections.
• Pre-infusion: verify platelet count ≥100 × 10⁹/L, neutrophils ≥1.5 × 10⁹/L.
• Imaging (Indium-111) to confirm targeting.

Summary

Ibritumomab (Zevalin®) is a CD20-targeted radioimmunotherapy for relapsed/refractory follicular or low-grade NHL. Its main concern is prolonged myelosuppression, with infusion reactions and infection risk. Requires coordination with nuclear medicine and adherence to radiation safety protocols.