rituximab (Rituxan) Side Effects, Uses, and Dosage

What is rituximab? How does it work (mechanism of action)?

• Rituximab is an intravenous drug that is used to treat rheumatoid arthritis and B-cell non-Hodgkin's lymphoma. It belongs to a class of drugs called monoclonal antibodies. Other monoclonal antibodies include trastuzumab (Herceptin) and gemtuzumab ozogamicin (Mylotarg). Tumor cells (like most normal cells) have receptors on their surfaces. Many kinds of chemicals, proteins, etc., on the outside of the cell can attach to these receptors. When they do, they can cause changes to occur within the cells. One receptor, present in more than 90% of B-cell non-Hodgkin's lymphomas, is called CD20. Molecules that attach to CD20 can affect the growth and development of the tumor cells and, sometimes, the production of new tumor cells. Rituximab is a man-made antibody that was developed using cloning and recombinant DNA technology from human and murine (mice or rat) genes. Rituximab is thought to attach to the CD20 receptor and cause the tumor cells to disintegrate (lyse). In some non-Hodgkin's lymphomas, it also prevents the production of more tumor cells.
• In the treatment of rheumatoid arthritis, rituximab is used when other biologic medications (TNF-blockers, such as infliximab, [Remicade] etanercept [Enbrel], or adalimumab [Humira]) have failed to be effective. The effectiveness of rituximab is a result of it temporarily depleting the number of B-cells, cells of the immune system that are important in promoting inflammation in rheumatoid arthritis.
• Rituximab was approved by the FDA in 1997.

What are the uses for rituximab?

Rituximab is used for the treatment of:

• Non-Hodgkin's B-cell lymphomas that have CD20 receptors on their surface. It is used when lymphomas recur following other types of therapy or are unresponsive to other types of therapy.
• Chronic lymphocytic leukemia
• Granulomatosis with polyangiitis
• Microscopic polyangiitis

Rituximab also is combined with methotrexate (Rheumatrex, Trexall) to treat rheumatoid arthritis in patients who have failed other biologic medications, such as infliximab (Remicade), etanercept (Enbrel), or adalimumab (Humira).

What are the side effects of rituximab?

• The most common side effect of rituximab is a constellation of symptoms (fever, rigors and chills) that occur during administration of the first dose of drug. More than 80% of patients experience these side effects, and it is severe in 4-7 out of every 10,000 patients. The side effects appear only 40% of the time with the second dose of drug and become less frequent with the last two doses.
• Other common side effects related to rituximab are:
  • Nausea
  • Hives
  • Fatigue
  • Headache
  • Itching
  • Difficulty breathing due to bronchospasm
  • A sensation of swelling of the tongue or throat
  • Runny nose
  • Vomiting
  • Decreased blood pressure
  • Flushing
  • Pain at the site of the tumor
• After rituximab is administered, large numbers of tumor cells are immediately destroyed (lysed) and eliminated from the body. In 4-5 out of every 10,000 patients the products from the dead cells cannot be eliminated quickly enough and a syndrome called tumor lysis syndrome occurs. This is characterized by a rapid decline in kidney function and a sudden accumulation or decrease in minerals such as potassium, calcium and phosphate to dangerous levels. Tumor lysis syndrome occurs when the size of the tumor or the number of tumor cells circulating in the blood is large, usually within 12-24 hours after the first dose of rituximab.
• Irregular heart rhythms and infection are two other rarely-occurring side effects that may be severe. The irregular heart rhythm usually begins soon after the administration of the drug, while infection may develop from 30 days to 11 months after the end of therapy. Severe decreases in red or white blood cells and platelets (thrombocytopenia) may occur rarely with rituximab therapy. Rituximab suppresses the immune system. Therefore, serious fungal, bacterial, and new or reactivated viral infections (for example, hepatitis B or C, shingles) can occur during or after treatment with rituximab. Generally, rituximab is avoided in the presence of active, significant infections. Rituximab may also cause severe skin reactions within 1 to 13 weeks after treatment is started. Rituximab therapy is not recommended if there is an allergy to mice or rats since rituximab is made in mice or rats and may contain minute amounts of rat or mice proteins that can lead to severe allergic reactions.

What is the dosage for rituximab?

• Rituximab is administered by intravenous infusion. Patients should receive acetaminophen (Tylenol) and an antihistamine prior to the infusion to reduce the severity of infusion reactions.
• Patients with rheumatoid arthritis also should receive methylprednisolone (Medrol, Depo-Medrol) 100 mg or a similar drug 30 minutes prior to the infusion to reduce the severity of infusion reactions.
• Non-Hodgkin's B-cell lymphomas: 375 mg/m2 weekly for 4 to 8 weeks or longer.
• Chronic lymphocytic leukemia: 375 mg/m2 for the first cycle then 500 mg/m2 every 28 days for cycles 2 to 6.
• Granulomatosis with polyangiitis or microscopic polyangiitis: 375 mg/m2
• Rheumatoid arthritis: Two 1000 mg infusions are administered two weeks apart and then are repeated every 16 to 24 weeks.

Which drugs or supplements interact with rituximab?

• Combining rituximab with cisplatin or amphotericin B (Fungizone) increases the risk of kidney failure.
• The combination of certolizumab pegol (Cimzia) with rituximab may increase immune suppression and risk of infections.

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Is rituximab safe to take if I’m pregnant or breastfeeding?

• There are not enough studies to draw conclusions about the safety of rituximab in pregnant women. Contraceptive methods are recommended if rituximab is used in women of childbearing age and for up to 12 months after stopping therapy.
• Since rituximab is an antibody that can be secreted into breast milk and absorbed by the infant, it has the potential for harming nursing infants. Women who are breastfeeding should avoid rituximab therapy and not begin nursing until rituximab is no longer present in the blood.

What else should I know about rituximab?

Rituximab is abailable as:

• Powder for intravenous injection: 100, 200, 500, 1000, and 2000 mg)
• Tabletss: 25, 50 mg.

Powder and tablets should be stored at room temperature, 15 C – 30 C (59 F – 86 F). Solutions prepared with bacteriostatic water are usable up to 24 hours if stored at room temperature and up to 6 days if stored in the refrigerator.

Rituximab is not available in generic form. You need a prescription for this drug.Rituxan is the brand name for rituximab in the US.