To evaluate real-world practice of cladribine use in people with multiple sclerosis (pwMS) in Northern Ireland.

Cladribine is a disease modifying therapy (DMT) licensed for treating highly active relapsing multiple sclerosis (RMS) in the UK since 2017. Recently a change in licensing for cladribine made it available for individuals with active RMS. There is limited real-world evidence of the use of cladribine and prevalence of post-treatment relapse.

We carried out a retrospective, observational study of the Northern Ireland DMT Register to identify patients treated with cladribine. Forty-three patients received cladribine between 2018 and 2024. Data collection included demographics, treatment dates, previous DMT use, relapses in previous year prior to cladribine, relapses post-cladribine and subsequent DMT use.

Forty-three patients were treated with cladribine (69.8% female). Three patients did not receive a second cycle. Nine patients were treatment naïve; 34 had previous treatment with at least one DMT. The median number of relapses in the year before starting cladribine was 1 (interquartile range [IQR]:1-2).

Eleven patients had a relapse post-cladribine, one of whom had not received their second year of treatment. In the remaining ten patients, the average time from treatment completion to relapse was 35.9 months (range 11 to 52 months).

Relapse symptoms included optic neuritis, transverse myelitis, monoparesis and sensory symptoms.  All patients who had relapse symptoms demonstrated new MRI activity. Subsequently, patients commenced ofatumumab (n=6), ocrelizumab (n=4), and natalizumab (n=1).

This study evaluated the Northern Ireland experience of cladribine use in patients with active RMS. Of those treated with cladribine, one quarter had a relapse with MRI activity, and following this received another highly effective DMT. The limitations of this observational study include a small sample size and relatively short median duration of follow up of 6 years, but highlight the importance of real-world data.