PB2250 IS ANTIMICROBIAL PROPHYLAXIS REQUIRED IN CHILDREN WITH IMMUNE THROMBOCYTOPENIA TREATED WITH RITUXIMAB?

Background: Childhood immune thrombocytopenia (ITP) is consider a benign disease; however, around 30% of affected children will have a chronic course (cITP) and a minority of them will develop severe refractoriness to first line therapies. As second line, eltrombobag, the thrombopoietin receptor agonist licensed for the treatment of chronic ITP in children, might be given but it is questioned whether it could provide durable platelet responses without continued dosing. In order to avoid splenectomy, the only proven therapeutic option for cITP, Rituximab (RTX) has been used as second line option, although not approved for ITP. However, since RTX depletes B cells by binding to the CD20 antigen surface markers, autoimmunity can be eradicated, thus treatment with this medication increases the risk of infections. Antimicrobial prophylaxis (AP) is used in patients with hematological malignancies receiving RTX but evidence is lacking for ITP. Aims: To report episodes of infections in children with ITP treated with RTX not having had received antimicrobial prophylaxis Methods: Medical files of children with ITP diagnosed and followed at our center from 2000 (when RTX was available) to December 2018 were retrospectively reviewed. The following data were collected for children found to have received RTX: demographics, chronicity of ITP (duration of thrombocytopenia >12 months), timing of RTX treatment after the onset of ITP, number of cycles and dose/week/cycle of RTX, absolute lymphocyte and B cell count pre and post RTX, duration of B cell elimination, clinical symptoms and signs of infection, and relevant laboratory or imaging confirmation of any infection. Parents inform consent had be given in all cases of RTX therapy. Results: E ight (4 males, 4 females), of a median age 8 years (range: 6 months – 15 years) at diagnosis of ITP, treated with RTX, at a median time of 19 months (range: 2‐ 48 months) from the onset of thrombocytopenia. All patients but one had cITP. All patients had previously received first line therapy (IVIG, cortisone); 3/8 had also received azathioprine. One child had already been splenectomized. RTX was administered according to the standard regimen (4 weekly doses of 375 mg/m 2 ). In one child, 100 mg/m 2 were administered the 3 rd and 4 th week, due to severe allergic reaction after the second dose. Seven patients received one cycle of RTX. In one child a second cycle of 4 weekly doses of RTX was given 7 months after the first one. The mean absolute lymphocyte/B cell count per cubic milimeter pre and post RTX was 1660/712 and 1627/3, respectively, whereas one child had none B cell depletion). The duration of B cell elimination was found to range from 1‐13 months. Antimicrobial prophylaxis was not administered to any child. All children returned to their activities.Only one child (12.5%) presented with fever, attributed to common cold four months after RTX therapy. Summary/Conclusion: In our study, none of the ITP patients treated with RTX received antimicrobial prophylaxis, mainly because of their young age and absence of comorbidities. None of the children presented with viral or fungal infection, despite B cell depletion for a quite long period of time.