To assess the early real-world safety, tolerability, and efficacy of cladribine tablets in relapsing-remitting multiple sclerosis (RRMS).

Cladribine tablets were recently approved for the treatment of RRMS based on evidence from Phase III trials. However, the real-world efficacy and safety of cladribine is unclear.

A retrospective chart review was performed to identify RRMS patients who initiated cladribine tablets prior to June 2019 at the MS Clinic in Toronto, Canada. Clinical features, reported side effects, lymphocyte nadir, and clinical/MRI disease activity after treatment initiation were collected.

111 RRMS patients who initiated cladribine tablets were identified, of which 14%(n=16) completed the two annual treatment courses. The median follow-up time after cladribine initiation was 284 days (range 41-512). All patients were previously treated with DMTs with 51%, 25%, 24% on 1, 2, or >3 prior DMTs respectively. The most common reasons prompting the switch to cladribine were: persistent relapses or MRI activity (57%, n=63), intolerance to prior DMT/patient choice (19, n=21) or AE related to prior DMT (13%, n=14). At a mean of 2.3 months after cladribine initiation, 10% (n=11) had one or more relapse. 65% (n=72) of patients showed evidence of lymphopenia at any time point after cladribine initiation: 16%(n=18) were grade 3 and 2%(n=2) demonstrated grade 4 lymphopenia. The mean time to lymphocyte nadir was 3.6 months. The most commonly reported side effects within 3 months of cladribine initiation were: flu/cold-like symptoms (8%) and nausea (6%). Three cases of herpes zoster infection were reported. There have been no treatment discontinuations to date.

Our early real-world experience demonstrates that cladribine tablets are generally well-tolerated and safe, with observed AEs consistent with what was reported in clinical trials. Prospective follow-up of this cohort will enable an assessment of the on-going safety and efficacy of cladribine in the real-world.