Lymphopenia associated with sphingosine 1-phosphate receptor modulators (S1PRMs) in multiple sclerosis: analysis of European pharmacovigilance data

Background: The treatment landscape for Multiple Sclerosis (MS) has increased significantly over the past few decades, thanks to the introduction of disease-modifying therapies (DMTs). Fingolimod, siponimod, ozanimod, and ponesimod belong to the newer generation of oral DMTs categorized as sphingosine 1-phosphate receptor modulators (S1PRMs). Because of their mechanism of action, they may increase the risk of lymphopenia, which could influence the therapeutic management of people with MS. The aim of this study was to describe and compare the reporting frequency of lymphopenia related to four S1PRMs. Methods: Individual case safety reports (ICSRs) were retrieved from the European spontaneous reporting system database (EudraVigilance) from January 1st, 2022, to December 31st, 2023. The reporting odds ratios (RORs) were computed to compare the reporting probability of lymphopenia between a S1PRM versus each other. Results: We retrieved 4017 ICSRs, of which 521 (13%) reported lymphopenia associated with fingolimod (53.3%), siponimod (38.4%), ozanimod (5.4%), and ponesimod (2.1%). The most common reporting source was the healthcare professional (94.2%), and more than half of the ICSRs (62.6%) reported serious lymphopenia. Fingolimod was associated with a lower reporting frequency of lymphopenia compared to siponimod. Both siponimod and fingolimod were associated with a higher reporting frequency of lymphopenia compared to ozanimod; siponimod also had a higher reporting probability in comparison with ponesimod. Conclusions: The most relevant clinical implication of the disproportionality analysis is to increase the awareness of the risk of lymphopenia related to these drugs, thus supporting proactive monitoring and optimizing treatment strategies for people with MS.