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What Is Rituximab?

Rituximab is a prescription monoclonal antibody that targets CD20, a protein found on certain B lymphocytes. It is used to treat selected B-cell blood cancers and immune-mediated diseases. Rituximab was first marketed in the United States as Rituxan, and several FDA-approved biosimilars are available. Most rituximab products are administered by intravenous infusion, while Rituxan Hycela combines rituximab with hyaluronidase for subcutaneous use in certain adult blood cancers. Treatment eligibility and approved indications depend on the specific product. Rituximab-containing medications can cause serious infusion reactions, infections, hepatitis B reactivation, and progressive multifocal leukoencephalopathy.

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What Is Rituximab?

Rituximab is a prescription monoclonal antibody that targets CD20, a protein found on certain B lymphocytes. It is used to treat selected B-cell blood cancers and immune-mediated diseases. Rituximab was first marketed in the United States as Rituxan, and several FDA-approved biosimilars are available. Most rituximab products are administered by intravenous infusion, while Rituxan Hycela combines rituximab with hyaluronidase for subcutaneous use in certain adult blood cancers. Treatment eligibility and approved indications depend on the specific product. Rituximab-containing medications can cause serious infusion reactions, infections, hepatitis B reactivation, and progressive multifocal leukoencephalopathy.

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How Does Rituximab Work?

Rituximab binds to CD20 on the surface of B cells, including malignant B cells in certain lymphomas and leukemias. Binding triggers immune processes that destroy CD20-positive cells, including complement-mediated and antibody-dependent cellular mechanisms. B-cell depletion helps reduce cancer cell populations and can suppress abnormal immune responses associated with certain autoimmune diseases. Rituximab does not directly target plasma cells that lack CD20 or every type of cancer. Its immune effects can continue for months after treatment, affecting infection susceptibility and responses to vaccination. The precise therapeutic contribution of different immune mechanisms varies by condition.

What Conditions Does Rituximab Treat?

Intravenous rituximab products are used for specified CD20-positive non-Hodgkin lymphomas and chronic lymphocytic leukemia, with some regimens involving chemotherapy. The reference product Rituxan also has approved indications for certain pediatric mature B-cell malignancies, rheumatoid arthritis in eligible adults, granulomatosis with polyangiitis, microscopic polyangiitis, and pemphigus vulgaris. Individual biosimilars may have different approved indications, age groups, or labeling requirements. In rheumatoid arthritis, rituximab is used with methotrexate in patients meeting the product's treatment criteria. Clinicians confirm the diagnosis, prior treatment history, and specific product indication before prescribing it.

How Is Rituximab Administered?

Intravenous rituximab is administered by trained healthcare professionals using indication-specific doses and schedules. Many lymphoma regimens use 375 mg/m? of body surface area on scheduled treatment days. For rheumatoid arthritis, a typical treatment course includes two 1,000 mg intravenous infusions given two weeks apart, with later courses based on clinical response. Other conditions require different induction or maintenance schedules. Patients receive premedication to reduce infusion reactions, and hepatitis B screening is required before treatment. Infusion rates are increased gradually according to the product instructions and patient tolerance. Rituximab should not be administered as an intravenous push or bolus.

What Are the Side Effects and Warnings of Rituximab?

Common adverse effects include fever, chills, fatigue, headache, nausea, and infusion-related reactions. Rituximab products carry serious warnings for potentially fatal infusion reactions, severe skin and mucosal reactions, hepatitis B reactivation, and progressive multifocal leukoencephalopathy. Other serious risks include infections, tumor lysis syndrome, heart rhythm abnormalities, kidney injury, and reduced blood cell counts. Patients may require infection screening, laboratory monitoring, and assessment of vaccination history before treatment. Sudden breathing difficulties, chest pain, severe rash, jaundice, confusion, or new weakness requires urgent medical evaluation. Risks and monitoring instructions can differ by product and treatment indication.

Common Questions About Rituximab

Is rituximab the same as Rituxan?

Rituxan is the original reference brand for rituximab. Several FDA-approved rituximab biosimilars are also available.

What is a rituximab biosimilar?

A rituximab biosimilar is a biologic shown to be highly similar to the reference product, with no clinically meaningful differences in safety, purity, or potency for its approved uses.

Can rituximab treat both cancer and autoimmune diseases?

Yes. Intravenous rituximab products have approved uses for selected B-cell cancers and certain autoimmune conditions, although indications vary by product.

Can rituximab reactivate hepatitis B?

Yes. Rituximab can reactivate hepatitis B infection, potentially causing severe liver injury. Patients require hepatitis B screening and appropriate monitoring.

References

DailyMed - RITUXAN (rituximab) injection. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b172773b-3905-4a1c-ad95-bab4b6126563. Date Accessed November 4, 2026.

Rituximab. LiverTox. https://www.ncbi.nlm.nih.gov/books/NBK548249/. Date Accessed November 4, 2026.

Rituximab. National Cancer Institute. https://www.cancer.gov/about-cancer/treatment/drugs/rituximab. Date Accessed November 4, 2026.

Rituximab. NCI Drug Dictionary. https://www.cancer.gov/publications/dictionaries/cancer-drug/def/rituximab. Date Accessed November 4, 2026.

Rituximab Injection. MedlinePlus. https://medlineplus.gov/druginfo/meds/a607038.html. Date Accessed November 4, 2026.