Immunoglobulin G1 (human-mouse monoclonal IDEC-C2B8 γ1-chain anti-human antigen CD 20), disulfide with human-mouse monoclonal IDEC-C2B8 κ-chain, dimer

Monoclonal antibody, immunoglobulin G anti CD20 composed of 664 amino acids. Indicated in the treatment of rheumatoid arthritis, non-Hodgkin's lymphoma, chronic lymphocytic leukemia, granulomatosis with polyangiitis (Wegener) and associated with methotrexate in severe active rheumatoid arthritis. Intravenous administration every week, two weeks or two months depending on the disease being treated.

It is excreted in breast milk in very small amounts ^{(Bosshard 2021, Krysko 2019, Bragnes 2017)} in line with its very high molecular weight, as is the case with other IgG1 monoclonal antibodies such as infliximab and adalimumab. ^{(Bragnes 2017, Fritzsche 2012)}

The plasma levels of infants whose mothers take them are no detectable. ^{(Bosshard 2021)}

An infant whose mother received a dose of 1 g of Rituximab at 3 months had no side effects at 1.5 years of follow-up ^{(Bragnes 2017)}. Five other infants had no problems after 8 to 12 months of follow-up ^{(Hersey 2020, Krysko 2019)}. The blood counts and immunoglobulins of 6 other infants were normal. ^(Rød 2022)

Due to its protein nature it is inactivated in the gastrointestinal tract, not being absorbed, (oral bioavailability practically null), which hinders or prevents the passage to infant plasma from the ingested breast milk ^{(Bragnes 2017, Götestam 2016, Butler 2014, Pistilli 2013)}, except in premature babies and the immediate neonatal period, when there may be greater intestinal permeability.

Based on its pharmacological properties, breastfeeding should not be discouraged when using rituximab if no other options are available ^{(Dobson 2023, Bosshard 2021, Krysko 2019, Whittam 2019, Götestam-EULAR 2016)}. Although previously not recommended during lactation ^{(Makol 2011)}, especially during the neonatal period and in case of prematurity ^{(Almas 2016, Ostensen 2009)}, more recently, various experts ^{(Dobson 2023, Bosshard 2021, Sammaritano 2020, Ciplea 2020, Krysko 2019, Bragnes 2017, Noviani 2016, Pistilli 2013)} consider safe or probably safe the use of this medication during lactation.

Given the strong evidence that exists on the benefits of breastfeeding for the development of babies and the health of mothers, it is advisable to evaluate the risk-benefit of any maternal treatment, including chemotherapy, individually advising each mother that wishes to continue with breastfeeding. ^{(Koren 2013)}

See below the information of these related products:

• Maternal Cancer (Unsafe. Moderate/severe adverse effects. Compatible under certain circumstances. Follow-up recommended. Use safer alternative or discontinue breastfeeding from 5 to 7 T ½ . Read Commentary.)
• Maternal Rheumatoid arthritis (RA) (Fairly safe. Mild or unlikely adverse effects. Compatible under certain circumstances. Follow-up recommended. Read Commentary.)