Introduction In ORACLE-MS (616 subjects with a first demyelinating event at high risk of converting to multiple sclerosis), cladribine tablets (CT) 10 mg (3.5 mg/kg or 5.25 mg/kg cumulative dose over 2 years) significantly delayed the time-to-conversion to clinically definite multiple sclerosis (CDMS), and reduced new/persisting T1 gadolinium-enhancing (T1 Gd+), new/enlarged or active T2 and combined unique active (CUA) lesion number. Here, the timing of CT effect is evaluated.

Methods MRI scans were performed at screening and every 12 weeks, for non-converting CDMS subjects. MRI-based endpoints were analyzed using analysis of covariance (ANCOVA) and negative binomial models. The temporal effects of the first yearly treatment course of CT and placebo on T1 Gd+, active T2, and CUA lesions were evaluated.

Results 96 weeks: the reduction in mean T1 Gd+, active T2, or CUA lesion number per patient per scan was nominally significantly greater for CT versus placebo (p<0.0001). Early change in Gd+ lesion volume (at Week 13) from baseline was CT, -155.73 mm³; placebo, -14.76 mm³. Comparatively larger reductions in mean active T2 and CUA lesion numbers with CT at Week 13 versus placebo were observed (active T2: CT, -1.25; placebo, -1.43; CUA: CT, -1.56; placebo, -2.41). The mean number of T1 Gd+ lesions at 13 weeks following CT was 0.37 versus 1.0 with placebo.

Conclusions MRI data from ORACLE-MS subjects suggest the first yearly treatment course of CT has a rapid onset of action, with beneficial treatment effects on active lesion number and volume evident by Week 13.