VANCOUVER, BC—The beneficial effects of cladribine for relapsing-remitting multiple sclerosis (RRMS) patients have been demonstrated to last for up to 4 years after treatment has started, those were the findings of a study presented at the 68th AAN Annual Meeting.

“After witnessing the clinically significant patient improvements in the two year cladribine ‘CLARITY’ trial, we extended the trial by a further two years to test the longevity,” reported lead study author Gavin Giovannoni, MBBCh, PhD, FCP, Queen Mary University of London, London, UK.

The initial CLARITY trial randomized patients to placebo or cladribine 3.5mg or 5.25mg depending on body weight. In the 2-year extension (Clarity-EXT) trial, patients who were in the placebo group in CLARITY were administered cladribine 3.5mg/kg. Also, patients who were previously administered cladribine were re-randomized 2:1 to cladribine 3.5mg/kg or placebo. This stratification created total of 5 separate treatment groups for assessment. After the extension period, patients entered a 6-month follow-up with an overall median duration of ~41 weeks. “This design allowed comparison of 2 treatment courses of cladribine tablets (2 years’ treatment + 2 years’ follow-up) vs. 4 treatment courses (4 years’ treatment),” described Dr. Giovannoni.

Study authors assessed annualized relapse rate (ARR), proportion of patients that were relapse-free, time to first qualifying relapse, proportion of patients free of Expanded Disability Status Scale (EDSS) progression, and time to confirmed EDSS progression. 

Generally, a low ARR was maintained over 2.5 years independent of cladribine dose or treatment order. Both CP arms (cladribine in CLARITY, placebo in CLARITY-ext) 3.5mg/kg and 7mg/kg showed comparable proportions of relapse-free patients (75.6% and 81.2%, respectively). Results showed that the patients treated with cladribine after 4 years had a ARR of 0.10 (97.5% CI: 0.06–0.13), those treated with cladribine in CLARITY and placebo in the extension had a ARR of 0.15 (97.5% CI: 0.09–0.21).

“We witnessed no significant differences between the groups in time to confirm any three month EDSS progression in the extension trial,” said Dr. Giovannoni. “However, the extension trial did demonstrate that the benefits witnessed in the first two years of cladribine use may extend for at least 4 years.”

The authors commented that further treatment should be based upon individual monitoring during this extended period.

This study was supported by Merck KGaA, Germany. Dr. Giovannoni currently serves on the Merck Serono advisory board, while the other authors have worked in the past for, or are currently employed with, Merck.