Background: In the Phase 3, 96-week ORACLE-MS study, cladribine tablets 10 mg (3.5 or 5.25 mg/kg cumulative dosage over two years) significantly reduced lesions associated with multiple sclerosis versus placebo in participants following a first clinical demyelinating event (FCDE).

Objective: To determine the timing of effects of cladribine tablets on lesion activity assessed by magnetic resonance imaging (MRI).

Methods: This post hoc analysis assessed the effect of cladribine tablets versus placebo in ORACLE-MS on secondary MRI endpoints including T1 gadolinium-enhancing (Gd+), new or enlarging T2 lesions, and combined unique active lesions assessed on MRI scans performed at screening and every 3 months thereafter.

Results: Compared to placebo, cladribine tablets 3.5 mg/kg treatment appeared to lead to a trend of reductions in the mean number of T1 Gd+ lesions by Week 13 (first post-baseline scan: 0.37 vs. 1.00), new or enlarging T2 (0.20 vs. 1.01) and combined unique active (0.29 vs. 1.91) lesions by Week 24. Low lesion counts were maintained with cladribine tablets throughout 96 weeks. Similar results were observed with the 5.25 mg/kg dosage.

Conclusions: In participants with an FCDE, cladribine tablets appeared to reduce lesion numbers within 13 weeks (time of first evaluation).