Analysis of frequency and severity of relapses in multiple sclerosis patients treated with cladribine tablets or placebo: The CLARITY and CLARITY Extension studies

Mult Scler. 2022 Jan;28(1):111-120. doi: 10.1177/13524585211010294. Epub 2021 May 10.


Background: In the CLARITY (CLAdRIbine Tablets treating multiple sclerosis orallY) study of patients with relapsing-remitting multiple sclerosis, treatment with cladribine tablets 3.5 mg/kg (CladT) significantly reduced the annualised relapse rate (ARR) versus placebo; this effect was sustained in CLARITY Extension, without further treatment.

Objective: To assess the frequency and severity of relapses in patients treated with CladT versus placebo in CLARITY over 2 years and evaluate the durability of effect in patients who received no further treatment for 2 years in CLARITY Extension.

Methods: In this post hoc analysis, ARRs were calculated for qualifying and all relapses, and qualifying and all severe relapses (i.e. requiring steroid treatment or leading to hospitalisation) in patients treated with CladT (n = 433) and placebo (n = 437) in CLARITY, and those from the CladT group who received placebo in CLARITY Extension (n = 98).

Results: At Month 6, Year 1 and Year 2, patients receiving CladT had a significantly lower risk of qualifying or all relapses (all p < 0.0001), and qualifying or all severe relapses (all p < 0.005), compared with placebo. This effect was sustained in CLARITY Extension without further treatment.

Conclusion: The results show durable efficacy of cladribine tablets 3.5 mg/kg for reducing frequency and severity of relapses in patients with relapsing-remitting multiple sclerosis.CLARITY: NCT00213135; CLARITY Extension: NCT00641537.

Keywords: Relapsing-remitting multiple sclerosis; cladribine tablets; disease-modifying therapy; hospitalisation; relapses; steroids.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cladribine / therapeutic use
  • Humans
  • Immunosuppressive Agents / therapeutic use
  • Multiple Sclerosis* / drug therapy
  • Multiple Sclerosis, Relapsing-Remitting* / drug therapy
  • Recurrence
  • Tablets


  • Immunosuppressive Agents
  • Tablets
  • Cladribine

Associated data