Rituximab is a drug used to destroy a subtype of the body's immune cells known as B cells. The medication does not discriminate between healthy and diseased cells, making it useful in the treatment of both autoimmune diseases like rheumatoid arthritis and cancers like leukemia and Hodgkin's lymphoma. Rituximab is also used as an off-label immunosuppressant to help prevent organ transplant rejection, although there have been no conclusive studies that show the drug is effective for this application. The rituximab dose recommendations vary depending on the condition to be treated as well as the patient's age, weight, drug regimen and medical conditions. Assessing the appropriate initial rituximab dose and subsequent dosage increases must be conducted with the utmost precision and careful premedication, as the drug frequently causes infusion reactions, which have the potential to be fatal.
When administering a solution of the drug intravenously, an initial rituximab dose of 50 mg per hour should be used, with increases of 50 mg per hour applied every half hour if there are no signs of an infusion or hypersensitivity reaction developing. If a reaction develops, the drug infusion should be slowed or stopped until the reaction subsides, and then increased at half the previous rate. The final dose should not exceed 400 mg per hour. If the patient does not exhibit any signs of an infusion reaction during the first course of treatment, subsequent treatments can be administered at a rate of 100 mg per hour and increased by the same dose every half hour.
When first treating CD20-positive, folicular B-cell non-Hodgkin's, or low-grade lymphoma, an initial regimen of 375 mg/m2 should be given intravenously on the first day of each chemotherapy cycle up to eight treatments. The same regimen should be used for patients with diffuse large B-cell non-Hodgkin's lymphoma. If the patient demonstrates either a complete or partial response to the therapy, an eight week weekly maintenance regimen should be followed in which rituximab is used as a monotherapy. When treating CD20-positive low-grade or folicular B-cell non-Hodgkin's lymphoma that has relapsed or persists, a rituximab dose of 375 mg/m2 should be given once weekly for between four and eight weeks. Re-treatment of the same condition requires only four weekly treatments at the same dosage level.
The dosage recommendations are somewhat different when using the medication to complement chemotherapy in chronic lymphocytic leukemia. The same rituximab dose of 375 mg/m2 should be given on the day prior to the initiation of fludarabine and cyclophosphamide chemotherapy. One important note, however, is that the first day of cycles two and six of chemotherapy require a higher dose of 500 mg/m2.
In patients with moderately severe to severe rheumatoid arthritis that have not responded adequately to at least one tumor necrosis factor (TNF) agonist therapy, a combination drug therapy may be used. In addition to the use of methotrexate, a 1,000 mg rituximab dose should be given once a week for two weeks, with subsequent courses of treatment considered every 24 weeks according to the response of the patient. Re-treatments should be conducted no sooner than every 16 weeks.
