The short answer
Rituxan (Rituximab) is a targeted therapy called a monoclonal antibody. It attaches to a marker called CD20 on certain white blood cells (B cells), flagging those cells — including cancerous ones — for destruction by the immune system. It is used to help treat some non-Hodgkin lymphomas and chronic lymphocytic leukemia (CLL), and is usually given as an IV infusion. Like all cancer medicines it can cause side effects; this page explains the common ones and the warning signs to report. It is educational only and not a substitute for your care team's advice.
Rituxan is the brand name; its generic name is rituximab.
It is a targeted therapy called a monoclonal antibody — it attaches to a marker called CD20 on certain white blood cells (B cells), flagging those cells — including cancerous ones — for destruction by the immune system.
It is used to help treat some non-Hodgkin lymphomas and chronic lymphocytic leukemia (CLL).
It is usually given as an IV infusion.
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The full explanation.
An antibody that clears CD20 B cells
B cells are the white blood cells that make antibodies. Nearly all of them carry a marker on their surface called CD20.
Rituximab is a lab-made antibody that latches onto CD20. Once it is attached, the immune system destroys the cell. Because the marker is on healthy B cells as well as cancerous ones, the treatment clears both. B cell numbers fall for months and then recover.
Rituxan is the brand name; rituximab is the generic name.
A hepatitis B test before the first dose
The FDA boxed warning says every patient must be screened for hepatitis B before treatment starts.
The reason is specific. If you have ever had hepatitis B, the virus can sit quiet in the liver for decades because B cells and antibodies keep it in check. Removing those cells can let it wake up. That reactivation has caused liver failure and death, sometimes months after the last dose.
The test is a simple blood test. If it is positive, treatment is often still possible, with antiviral medicine and liver monitoring alongside. What is not safe is skipping the test.
The first infusion is the one to watch
Serious, sometimes fatal reactions can happen during the drip. About 80% of the fatal ones in the boxed warning happened with the very first infusion.
So the first one is given slowly, often over several hours. You get acetaminophen and an antihistamine first. A nurse stays close by. Later infusions are usually faster.
Speak up immediately for a tight throat, wheeze, chest pain, sudden dizziness, a swollen tongue or lips, or a rash coming up during the drip. The infusion can be stopped and restarted more slowly.
The rest of the boxed warning
Two more risks sit in that box.
Severe skin and mouth reactions, some fatal, have occurred. Blistering, peeling skin, painful mouth or eye sores, or a spreading rash need urgent review.
PML is a rare brain infection that has been fatal. The full name is progressive multifocal leukoencephalopathy. It builds over days or weeks. Signs include new confusion, clumsiness, weakness on one side, changes in vision, and trouble finding words. Tell your team at once.
The blood cancers on the label
In adults with non-Hodgkin lymphoma, the label covers four settings. Low-grade or follicular CD20-positive disease that came back or did not respond. Untreated follicular lymphoma, with chemotherapy and then on its own as maintenance. Low-grade disease that is stable after CVP chemotherapy. And untreated diffuse large B-cell lymphoma, with CHOP or a similar regimen.
Children from 6 months of age can have it with chemotherapy. That use covers untreated advanced CD20-positive diffuse large B-cell lymphoma, Burkitt lymphoma, Burkitt-like lymphoma, and mature B-cell acute leukemia.
In adults with chronic lymphocytic leukemia, it is approved with fludarabine and cyclophosphamide. That holds whether or not the person has had earlier treatment.
It is not only a cancer drug
Rituximab is also approved for rheumatoid arthritis. It is approved for two kinds of blood vessel inflammation, called granulomatosis with polyangiitis and microscopic polyangiitis. And it is approved for a skin condition, pemphigus vulgaris.
If you search the drug's name you will find pages written for those conditions instead. The doses and schedules are different. Check which one you are reading.
Biosimilars and the under-the-skin version
You may be given rituximab-abbs, rituximab-pvvr or rituximab-arrx. These are biosimilars. A biosimilar is a closely matched version, approved on its own evidence. The letters on the end tell the products apart. They do not mean a lower standard.
There is also a form injected under the skin over several minutes, mixed with an enzyme. It is used only after a first full dose has been given into a vein.
Infection risk after treatment ends
B cells stay low for months, so antibody levels can fall. The label reports serious infections in people whose levels stayed low for more than 11 months. Some of those were old viruses waking up again.
Ask your team about vaccines. The label says live vaccines are not recommended before or during treatment. Your vaccination record is worth reviewing before you start.
When to get help sooner
- Call 911 or go to an emergency department if your throat tightens, your tongue or lips swell, you wheeze, or you feel faint during an infusion or in the hours after one. Tell staff at once if this starts while you are still in the chair.
- Phone your care team without delay, day or night, if you run a temperature of 100.4°F (38°C) or higher, or get shaking chills, while you are having rituximab with chemotherapy. Fever during chemotherapy is a medical emergency. If you cannot reach them quickly, go to an emergency department and tell staff you are on chemotherapy.
- Call 911 or go to an emergency department if you become confused, weak down one side, unsteady on your feet, or unable to find words or see properly. These can be signs of PML, and they need to be assessed straight away.
- Call your care team the same day if your skin or eyes turn yellow, your urine goes dark, or you feel sick and very tired with pain under your right ribs. Hepatitis B can wake up months after the last dose, so say that you have had rituximab. Ring the same day too for blistering or peeling skin, or raw sores in your mouth or eyes.
- Call your care team within a day or two if you pick up an infection that will not clear, or coughs and chest colds keep coming back. Antibody levels can stay low long after your last dose.
Sources
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b172773b-3905-4a1c-ad95-bab4b6126563
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3e5b7e82-f018-4eaf-ae78-d6145a906b20
- https://www.cancer.gov/about-cancer/treatment/drugs/rituximab
- https://www.cdc.gov/cancer-preventing-infections/patients/fever.html
Words to know
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Common questions
What is Rituxan?
Rituxan (Rituximab) is a targeted therapy called a monoclonal antibody. It attaches to a marker called CD20 on certain white blood cells (B cells), flagging those cells — including cancerous ones — for destruction by the immune system. It is used to help treat some non-Hodgkin lymphomas and chronic lymphocytic leukemia (CLL).
How is Rituxan given?
It is usually given as an IV infusion. It is given as an intravenous (IV) infusion — a slow drip into a vein — at a clinic or hospital, usually repeated on a schedule of cycles with rest periods in between. The exact schedule is set by your care team.
What are the common side effects of Rituxan?
Commonly reported side effects include fever or chills with infusions, tiredness, nausea, low blood counts, and body aches. Not everyone gets them, and many can be managed. Tell your care team about anything new or worsening.
Does Rituxan cure cancer?
That depends on the person, the cancer type, and its stage. For some people a medicine like this can control cancer for a long time or be part of a curative plan; for others the goal is to slow the cancer or ease symptoms. Your care team can explain the goal in your situation.
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Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-18Next planned review: 2027-01-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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