Cancer drugs known as monoclonal antibodies are sometimes know as targeted therapies because they target specific receptors on the surface of cells, and Rituximab is one of these drugs. Rituximab is a drug which destroys B cells in the blood. It locks on to a particular protein called CD20 which is found on the surface of white blood cells (also known as B-lymphocytes or B cells). It is found on the surface of both normal and abnormal B cells. The antibodies in the Rituximab bind to the B cells and kills them off. This then allows a new population of healthy B cells to develop from lymphoid stem cells once the treatment is over. It is therefore used to treat diseases which have excessive, dysfunctional or overactive B cells. This includes many lymphomas, leukemias and auto-immune diseases, such as Wegener's Disease.
Rituximab is a colourless fluid which is given intravenously. Some people have an allergic reaction to the drug so the first infusion is normally given over a period of several hours. You may be asked to stay in hospital overnight so that you can be monitored. If your first course goes well, further infusions may be given over shorter periods in the outpatient department.
Rituximab has a number of serious possible side effects including cardiac arrest, acute renal failure, susceptibility to infections - particularly progressive multifocal leukoencephalopathy, and pulmonary toxicity. As Rituximab destroys both healthy and abnormal white blood cells it means the body cannot fight off infection effectively once treatment begins. A low white blood cell count is called neutropenia.
Your blood may not clot properly as the number of platelets your body produces are reduced. This may lead to nosebleeds, bleeding gums, and unexplained bruises.
Rituximab can reduce the number of red blood cells as well as the white blood cells in your blood. This can lead to fatigue and breathlessness and is known as anemia.
The trade names of Rituximab are Rituxan and Mabthera. The drug was developed by IDEC Pharmaceuticals and following clinical trials it was approved in the U.S.A. in 1997 for the treatment of B cell non-Hodgkins lymphomas which were resistant to other chemotherapy drugs. It was approved by the European Commission in 2010 for the maintenance treatment of follicular lymphoma.
Rituximab is used in the U.S.A. and Europe in the treatment of Rheumatoid Arthritis. It is also used off-label to treat multiple sclerosis, lupus, Evans syndrome, and of course vasculitis, including Wegener's Granulomatosis. A study in Norway in 2011 even indicated that Rituximab may be useful in treating Chronic Fatigue Syndrome which in turn led some to link the syndrome to auto-immune diseases. However this study was tiny and further investigation is certainly needed. Rituximab is also used as an anti-rejection drug for organ transplants.
Rituximab is a costly treatment. a 50ml vial for for infusion costs around £1000 in the UK.
The use of Rituximab in treating Wegener's Granulomatosis is an exciting development, but it should be viewed with caution. The short term side effects may be better for some sufferer's than the alternative treatment of low-level chemotherapy drugs, but the side effects can still be very serious and as the drug has been used to treat GPA for a relatively short period of time, no-one knows what the long term consequences might be.
Photograph provided by NIAID under Creative Commons.