Low level of Rituximab in human breast milk in a patient treated during lactation

Sir, Rituximab (RTX) is a chimeric mAb specifically targeting CD20 on B cells that induces the depletion of mature B cells and B cell precursors. The mean terminal elimination half-life in patients with vasculitis has been found to be 23 days (range: 9–49 days). In an animal study RTX was detected at low levels in breast milk of cynomolgus monkeys with concentrations of 0.19 and 0.26% of maternal serum level [1]. In two recent consensus papers breastfeeding when treated with RTX was not recommended because of lack of data [2, 3]. Since there are no publications on the excretion of RTX into human breast milk, serum and milk samples of a patient with granulomatosis with polyangiitis who had received RTX during her lactation period were analysed. The patient is a 34-year-old women with onset of granulomatosis with polyangiitis in 2011. Because of glomerulonephritis, diffuse alveolar haemorrhagia in the lungs, sinusitis and skin vasculitis she was treated with RTX (1000 mg twice), CYC (1000 mg once) and metylprednisolone pulses of 1000 mg three times, followed by 60 mg prednisolone per orally. After achieving remission and because of intolerance to AZA, she was treated with MTX 20 mg weekly for maintenance therapy combined with low dose prednisolone. The patient stopped MTX in April 2013 because of her wish to have a child. She had several moderate flares with skin vasculitis, musculoskeletal and general symptoms, as well as persisting PR3 ANCA antibodies during the first 6 months after stop of MTX. A new RTX infusion of 1000 mg in May, and 1000 mg in June 2014 was given 2 weeks apart. The patient became pregnant in November 2014, 5 months after the last RTX infusion. She continued 5 mg of prednisone throughout the course of pregnancy, which was uncomplicated. She delivered a healthy baby girl at term 2015. The child was fully breastfed, had no serious infections during the lactation period and developed normally during a 1.5 year follow-up.