In CLARITY and CLARITY Extension (NCT00213135 and NCT00641537, respectively), treatment with cladribine tablets 10 mg (cumulative dose 3.5 mg/kg over 2 years [CT3.5]) significantly reduced relapse rates in patients with relapsing-remitting multiple sclerosis. Moreover, in the CLARITY Extension study, treatment with cladribine tablets for 2 years followed by treatment with placebo for 2 years produced similar clinical benefits to 2 years of cladribine tablets treatment followed by an additional 2 years of treatment, but with a lower risk of higher grade lymphopenia.
To assess, post hoc, the temporal occurrence of relapses up to 5 years after treatment initiation with cladribine tablets.
Patients enrolled into CLARITY treated with CT3.5, and those subsequently receiving CT3.5 (CC7) or placebo (CP3.5) in CLARITY Extension, were included for analysis. The main endpoint was all qualifying relapses reported in CLARITY or CLARITY Extension plus those that occurred during the variable bridging interval (range: 1 day to 118 weeks). A recurrent event analysis was performed to estimate mean cumulative number of relapses over time using a cumulative mean function estimate.
A total of 433 patients from CLARITY treated with CT3.5 were included in this analysis; of these 284 patients entered CLARITY Extension (CP3.5, n=98; CC7, n=186). Recurrent event analysis for the CT3.5 population showed that annual increase in mean cumulative number of relapses was consistently low from Year 2 to Year 5 (range: 0.10–0.15) and was slightly higher in Year 1 (0.17); the 6-month increase in mean cumulative number of relapses was similar in the first 6 months and the second 6 months (0.08 and 0.09, respectively). There were no differences in mean cumulative number of relapses between the CP3.5 and CC7 groups from Year 2 to Year 5. In recurrent event analysis for the CT3.5 population, the yearly increments of mean cumulative function were constant and low from the second treatment to Year 5, supporting the durable efficacy of cladribine tablets (given no increase in relapses following completion of the two courses of cladribine tablets).
Annual increase in mean cumulative number of relapses occurred at a low annualized rate of 0.10 to 0.17 per year to 5 years, almost 4 years after the last dose of cladribine tablets and therefore consistent with durable efficacy. Results also support the early effect of cladribine tablets on relapses, which is apparent in the first year of treatment.