Background: Cladribine, a deoxyadenosine analogue prodrug that preferentially depletes lymphocytes, may disrupt the central immune cascade in persons with multiple sclerosis (MS) Cladribine tablets are a short-course oral disease-modifying drug (DMD) administered in four four-to-five-day courses over two years. Cladribine tablets are indicated for the treatment of adults with relapsing forms of MS based on data from pivotal clinical trials, including the phase 3 study, CLARITY, and its extension. Objectives: Our study aims to present early real-world experience in aging MS patients previously treated with other DMDs switched to cladribine. Understanding the benefit/risk profile of using a non-continuous immunosuppressive DMD in this population is of the utmost importance given immunosenescence and the increased risk of comorbidities with age. Outcomes presented include patient characteristics at treatment initiation, previous DMD use, safety, lymphocyte counts, and preliminary efficacy data. Methods: Retrospective chart review reporting on 48 patients who have initiated therapy with cladribine tablets. Results: All patients were previously treated with a DMD. Median age at cladribine tablets initiation was 51.5 years (range 29-72) with median disease duration of 12.5 years (range 1-26). Mean follow up was 427 days and 40% of patients completed both treatment courses by data cut-off. 76% of patients experienced lymphopenia with 2 patients (4.3%) experiencing grade 4 lymphopenia. Overall, cladribine tablets were well tolerated. Upper respiratory tract infection and urinary tract infection occurred in ? 5% of patients. Conclusions: In this cohort of patients initiating therapy with cladribine tablets in a real-world setting, the treatment was well-tolerated. There were no new safety signals. The side effect profile was consistent with that seen in the clinical trial program, even in an aging patient population where co-morbid conditions and immunosenescence may increase. Owing to short follow-up time, it was not possible to assess long-term outcomes. Ongoing follow-up will further expand on these results as more patients complete their full treatment course.