Rituximab is a monoclonal antibody medication designed to target specific cells within the body. It interacts with components of the immune system to address certain medical conditions with precision.
How Rituximab Works
Rituximab functions by precisely targeting a protein called CD20, found on the surface of certain immune cells called B-lymphocytes. This protein is present on B-cells at various stages of their development, from early pre-B cells to mature B-cells. CD20 is absent on hematopoietic stem cells and fully developed plasma cells, which regenerate B-cells and produce antibodies.
When rituximab binds to CD20 on a B-cell, it triggers several mechanisms that eliminate the cell. These include antibody-dependent cellular cytotoxicity (ADCC), where immune effector cells destroy targeted B-cells. Complement-dependent cytotoxicity (CDC) activates part of the immune system to puncture the B-cell membrane. Rituximab also directly induces apoptosis, or programmed cell death, in these targeted B-cells.
Conditions Treated by Rituximab
Rituximab treats various medical conditions, including specific types of cancer and autoimmune disorders. In cancers like non-Hodgkin lymphoma and chronic lymphocytic leukemia, B-cells can become cancerous and multiply uncontrollably. By depleting these CD20-positive B-cells, rituximab helps reduce tumor burden and control disease progression.
For autoimmune diseases, rituximab addresses conditions where the immune system mistakenly attacks the body’s own tissues. In rheumatoid arthritis, B-cells contribute to inflammation and joint damage by producing harmful autoantibodies. Depleting these B-cells reduces autoantibody production, alleviating symptoms and slowing disease progression.
Rituximab is also used for granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA), which are conditions involving inflammation of blood vessels. In these disorders, B-cell activity contributes to the inflammatory process, and their depletion can help manage the disease. Rituximab also treats pemphigus vulgaris, a rare autoimmune disorder causing painful blisters on the skin and mucous membranes, where B-cells produce antibodies that attack skin components.
Receiving Rituximab Therapy
Rituximab is administered as an intravenous (IV) infusion, meaning the medication is delivered directly into a vein. This process takes place in a specialized outpatient clinic or a hospital infusion center. Healthcare professionals carefully monitor patients throughout the infusion session.
The duration of an infusion session can vary, generally lasting between two to four hours, though some infusions might take longer. For a first infusion, the rate of administration begins slowly, around 50 milligrams per hour, and is gradually increased every 30 minutes, up to a maximum rate of 400 milligrams per hour. Subsequent infusions start at a faster rate, such as 100 milligrams per hour, also increasing incrementally.
The frequency of rituximab treatments depends on the specific condition being addressed. For some lymphomas, treatment involves weekly infusions for four to eight doses. In rheumatoid arthritis, a common regimen involves two 1000 milligram doses given two weeks apart, with maintenance infusions administered every six months. Patients receive pre-medications, such as acetaminophen, antihistamines, and corticosteroids like methylprednisolone, before each infusion to minimize infusion-related reactions.
Potential Side Effects and Management
Patients receiving rituximab therapy may experience various side effects, with infusion-related reactions being common. These reactions often occur during the first infusion or within 24 hours afterward and can include symptoms such as:
Fever, chills, shivering, itching, rash
Fatigue, nausea, headache, muscle spasms
Low blood pressure, dizziness, swelling of the face, lips, or throat
Weakness, heart palpitations, or chest discomfort
Healthcare providers closely monitor for these reactions during and after the infusion, and the infusion rate may be slowed or temporarily stopped if they occur.
The depletion of B-cells by rituximab can increase the risk of infections, including bacterial, fungal, and viral types. Reactivation of hepatitis B virus in previously infected individuals is a serious, though less common, concern. A rare but severe brain infection, progressive multifocal leukoencephalopathy (PML), has also been reported. It is characterized by symptoms such as confusion, dizziness, loss of balance, difficulty speaking or walking, weakness on one side of the body, and vision problems.
Other less common but serious side effects include severe skin and mouth reactions, which can manifest as blistering, peeling skin, or painful sores. Cardiac events, such as chest pain or irregular heartbeats, have also been noted. For patients with certain cancers, tumor lysis syndrome is a possibility. This condition, caused by the rapid breakdown of cancer cells, can lead to kidney problems indicated by rapid weight gain, swelling, or changes in urine output. Medical teams monitor for these effects and implement management strategies, such as providing aggressive hydration for tumor lysis syndrome, to ensure patient safety.