Lymphocyte dynamics in patients with multiple sclerosis who were treated with dimethyl fumarate and subsequently switched to diroximel fumarate

• Switching between fumarates is common during relapsing multiple sclerosis treatment. • Absolute lymphocyte count dynamics were studied in Switchers and Stayers. • Lymphocyte counts decreased 26.9 % in Switchers and increased 3.5 % in Stayers. • Infection rates were similar in Switchers and Stayers regardless of lymphopenia. • Lymphocyte count monitoring is useful for managing fumarate-treated patients. Dimethyl fumarate (DMF) and diroximel fumarate (DRF) are oral multiple sclerosis (MS) disease-modifying therapies (DMTs). Absolute lymphocyte count (ALC) dynamics are similar for DMF and DRF, but have not been investigated in patients who switched from DMF to DRF. This retrospective, observational study of the US Komodo Health Claims Database characterized ALC dynamics and outcomes in patients who switched DMF-DRF (“Switchers”) versus patients who stayed on DMF (“Stayers”). Eligible patients aged 18–64 years, with a diagnosis of MS and ≥1 DMT claim during the study period (01Jan2015 31Aug2022) had ≥1 year on DMF before switching to DRF and ≥6 months on DRF. Switchers were propensity score-matched 1:2 to Stayers. Assessments included ALC, relapses, and infection-related healthcare encounters (HCEs) and healthcare costs (HCCs). Of 94 eligible Switchers, 62 were matched with 124 Stayers. Mean (SD) duration of DMF exposure was 36.0 (16.0) months prior to index date/switch and 15.0 (4.9) months post-index date/switch. Over 12 months, mean ALC change from index date was –26.9 % (Switchers) versus +3.5 % (Stayers). In Switchers, mean ALC remained stable thereafter. Proportions remaining relapse-free during 15 months mean follow-up were similar between Switchers (95 %) and Stayers (91 %). Outcomes were similar for annualized rates of infection-related HCEs (mean [SD]: Switchers, 0.70 [1.03]; Stayers, 0.74 [1.57]) and HCCs (mean [SD]: Switchers, $285 [$856]; Stayers, $346 [$2299]). Over 12 months, ALC declined by 26.9 % in Switchers but increased by 3.5 % in Stayers. Despite this difference in ALC dynamics, infection-related HCEs and HCCs remained low and comparable between cohorts.