Author: Anoma Ranaweera B.V. Sc, PhD, Clinical Biochemistry, University of Liverpool, UK. Reviewed and updated by Amanda Oakley, Dermatologist, 22 February 2014.
What is rituximab?
Rituximab is a monoclonal antibody directed against the CD20 antigen found on the surface of normal and malignant B lymphocytes. Rituximab has human and mouse-derived components. It is given by intravenous injection.
Rituximab is very effective at destroying normal and malignant B lymphocytes that are carrying the CD20 antigen.
Trade names used in New Zealand for rituximab include Mabthera (Roche) and Rituximab (Baxter). Rituxan is the name used for the Genentech product available in the USA and elsewhere.
B lymphocytes are a type of white blood cell. Their role in immune reactions includes:
Rituximab is an immunoglobulin G1 (IgG1) kappa monoclonal antibody composed of a murine (mouse) variable region (Fab portion) that is fused onto a human constant region (Fc portion). The Fab portion binds to the CD20 antigen on the surface of pre-B and mature B lymphocytes. The Fc portion then recruits immune cells that destroy these lymphocytes. Mechanisms may include:
The exact contribution of each mechanism remains unclear, and different mechanisms may prevail in different diseases.
Rituximab has limited effect on other immune cells.
Rituximab is approved by Medsafe in New Zealand for:
PHARMAC provides limited funding for rituximab to include some cases with:
Rituximab has also been found to be useful in a variety of immune-mediated and autoimmune skin disorders in which traditional therapy has failed or resulted in side effects. However, the efficacy, tolerability and dosing of rituximab in the treatment of dermatologic disease is not yet clear.
To date, rituximab has been reported to be effective in at least some cases with the following skin conditions:
Cutaneous B-cell lymphoma includes follicle centre, marginal zone, and diffuse large B-cell lymphoma, which have all been reported to respond to intravenous rituximab. Direct injections into the skin lesions has also been successful allowing a lower dose to be used. However, after initial response, the lymphoma may recur within several months. Retreatment may or may not prove successful as lymphomas can lose CD20 expression and, with that, susceptibility to rituximab.
Primary blistering diseases (also called autoimmune bullous diseases) are associated with autoantibodies directed against various structural support proteins in the epidermis and dermoepidermal junction.
Rituximab has been successfully used for treatment-resistant cases of:
Dermatomyositis is an autoimmune disease characterised by inflamed, weakened muscles associated with a characteristic rash. How this occurs is unknown but it involves T cells, B cells and antibodies directed against the endothelial cells lining blood vessels in the muscles.
Treatment of treatment-resistant dermatomyositis with rituximab has led to improvement of muscle and skin disease in several patients. Clinical trials have been set up to determine the role of rituximab in dermatomyositis.
Chronic graft versus host disease (GVHD) affects 60-70% of long-term survivors after bone marrow transplantation. It results in lichenoid and sclerodermatous skin changes as well as disease of internal organs. GVHD often fails to respond to conventional treatment and a quarter of the patients die from it.
Chronic GVHD has been thought to be due to donor T cells but drugs targeting T cells have not proved very effective. There is now mounting evidence that B cells are responsible. There have been reports of improvement with rituximab in some patients with GVHD.
Vasculitis is classified as a type-III hypersensitivity reaction involving immune complexes, i.e., antibodies bound to antigens in the affected blood vessels. Exactly how rituximab works in vasculitis is unknown.
In April 2011, the US FDA approved rituximab for antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (Granulomatosis with polyangiitis and microscopic polyangiitis). Case reports suggest rituximab is also efficacious in cutaneous vasculitis due to cryoglobulinaemia.
Atopic dermatitis (eczema) results from a complex interaction between various immune cells and proteins and in many patients is characterised by high levels of serum IgE. B cells and plasma cells produce IgE, so theoretically, B cell depletion could help treat the disease.
Rituximab has resulted in impressive improvement of atopic dermatitis in some patients with severe disease. However, although researchers confirmed reduction in circulating B cells in their patients, they found little change in IgE levels.
Rituximab has been successfully used to treat refractory cutaneous lupus erythematosus.
Most patients experience mild-to-moderate side effects from their first infusion of rituximab. The most common symptoms are:
The symptoms usually settle if the infusion is stopped temporarily and tend to be less severe with subsequent infusions. Pretreatment with paracetamol and antihistamines is recommended. Corticosteroid may also be used.
Some patients have died from infection after rituximab infusions due to:
Patients should be urged to seek prompt medical attention if they develop new neurological symptoms such as changes in vision, balance or thought processes.
Other deaths from rituximab have been due to:
Many other less serious adverse reactions have been reported, including a variety of rashes and:
The use of rituximab in children and in patients with kidney or liver failure has not been studied extensively. Rituximab should be avoided during pregnancy unless the potential benefit justifies the potential risk to the fetus (Pregnancy Risk Category C). Breast-feeding mothers should be advised to discontinue nursing until circulating blood levels are no longer detectable.
Current safety information is based on treatment for non-Hodgkin lymphoma and rheumatoid arthritis and may not be applicable when rituximab is used for other disorders.
The usual dose of rituximab is 375 mg for every square metre of body surface area, given intravenously over several hours, once weekly for several weeks. Regimes have varied for the skin diseases described above.
Blood count should be monitored.
Rituximab is not recommended for treatment of patients with severe active infections.
Though there have been no formal drug interaction studies performed with rituximab, the concomitant use of rituximab and cisplatin should be avoided as this combination has been associated with renal failure.
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