RITUXAN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for RITUXAN (RITUXAN).
Rituximab is a chimeric monoclonal antibody that binds specifically to the CD20 antigen on pre-B and mature B-lymphocytes. Binding induces complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC), leading to B-cell depletion.
| Metabolism | Rituximab is a monoclonal antibody and is not metabolized by cytochrome P450 enzymes; it is degraded via catabolic pathways into small peptides and amino acids. |
| Excretion | Rituximab is eliminated primarily via reticuloendothelial system metabolism and target-mediated clearance. Renal excretion is negligible (<1% of dose as intact antibody in urine). Biliary/fecal excretion is minimal. Clearance is influenced by tumor burden and CD20 expression. |
| Half-life | Mean terminal elimination half-life is approximately 22 days (range 6.1–52 days) after first dose, decreasing to about 6 days after fourth dose due to target-mediated clearance. Clinical context: Extended half-life allows for weekly or every-2-week dosing; half-life shortens with repeated dosing due to B-cell depletion. |
| Protein binding | Rituximab is a monoclonal antibody; specific protein binding is not characterized. Binding to FcRn may influence half-life. No significant binding to plasma proteins other than antigen targets. |
| Volume of Distribution | Volume of distribution at steady state (Vdss) is approximately 3.1–4.5 L (0.04–0.06 L/kg for a 70 kg patient), indicating limited extravascular distribution, primarily confined to plasma and interstitial fluid. Clinical meaning: Low Vd reflects distribution mainly in central compartment; minimal penetration into tissues. In non-Hodgkin lymphoma, Vd may be higher due to tumor binding. |
| Bioavailability | Intravenous: 100% bioavailability. Not available for subcutaneous, intramuscular, or other routes; no oral formulation due to protein degradation. |
| Onset of Action | Intravenous: Onset of clinical effect (B-cell depletion) occurs within hours to days. Maximal B-cell depletion in peripheral blood is observed by 2–3 weeks after first infusion. Clinical response in rheumatoid arthritis may be seen within 8–16 weeks. |
| Duration of Action | Duration of B-cell depletion is 6–12 months after a single treatment course (e.g., 2 infusions). Clinical duration varies: in oncology, response may last months to years; in autoimmune conditions, retreatment is often needed every 6–12 months. Recovery of B-cell counts begins approximately 6 months after completion of therapy. |
375 mg/m2 IV weekly for 4 doses for non-Hodgkin lymphoma; 1000 mg IV on days 1 and 15 for rheumatoid arthritis; 375 mg/m2 IV weekly for 4 doses for chronic lymphocytic leukemia (in combination with fludarabine and cyclophosphamide).
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment; not removed by hemodialysis. |
| Liver impairment | No specific guidelines for Child-Pugh; use caution in severe hepatic impairment as it has not been studied. |
| Pediatric use | Safety and efficacy not established in pediatric patients for most indications; use in pediatric nephrotic syndrome: 375 mg/m2 IV weekly for 4 doses. |
| Geriatric use | No specific dose adjustment; monitor for increased risk of infections and cardiac events. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for RITUXAN (RITUXAN).
| Breastfeeding | Rituximab is excreted in human breast milk in very low concentrations; the milk-to-plasma ratio is unknown. Limited data suggest minimal oral bioavailability due to digestion in the infant gastrointestinal tract. The American Academy of Pediatrics considers rituximab compatible with breastfeeding, but caution is advised given the potential for immunosuppression in the infant. The half-life in breast milk is short, and exposure is likely minimal. |
| Teratogenic Risk | First trimester: There is a theoretical risk based on mechanism (B-cell depletion), but human data are limited. Rituximab is an IgG1 antibody that crosses the placenta in the second and third trimesters, with highest fetal exposure in the third trimester. Second/third trimester: Cases of transient neonatal B-cell lymphopenia and cytopenias have been reported; however, no consistent pattern of major congenital malformations has been observed. Overall risk is considered low, but B-cell depletion in neonates is possible. |
■ FDA Black Box Warning
WARNING: Fatal infusion reactions, severe mucocutaneous reactions, progressive multifocal leukoencephalopathy (PML), and hepatitis B reactivation.
| Serious Effects |
Hypersensitivity to rituximab or any component of the formulation; active severe infections (e.g., hepatitis B, tuberculosis); severe immunocompromised state; caution in patients with history of cardiac disease or pulmonary insufficiency.
| Precautions | Infusion reactions (fatal within 24 hours), tumor lysis syndrome, severe mucocutaneous reactions (e.g., Stevens-Johnson syndrome), hepatitis B reactivation (screen high-risk patients), progressive multifocal leukoencephalopathy (PML), cardiac arrhythmias, renal toxicity (in combination with chemotherapy), bowel obstruction/perforation, and vaccination limitations (live vaccines not recommended during treatment). |
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| Fetal Monitoring | Maternal: Monitor for infusion reactions, infections, and cytopenias. Fetal/neonatal: If used after 20 weeks gestation, monitor neonatal complete blood count (CBC) at birth and for signs of infection or hematologic abnormalities. Because of the risk of B-cell depletion, avoid live vaccines in infants for at least 6 months after last maternal dose. |
| Fertility Effects | In women, rituximab may cause ovarian failure and reduced fertility based on cases of ovarian insufficiency reported in premenopausal women. In men, no specific effects on sperm have been documented; however, animal studies show no impairment of fertility. Effect on fertility appears to be reversible in some cases. |