Background Switching between first-line disease-modifying therapies in patients with clinically stable relapsing–remitting multiple sclerosis (RRMS) due to reasons other than disease activity is frequent, but evidence on the effect of this practice is limited. We investigated the effect of switching patients with stable RRMS on occurrences of disability accumulation, relapses and future treatment discontinuation.

Methods Using the Danish Multiple Sclerosis Registry, we identified patients with RRMS without disease activity who either (1) stayed on injectable platform therapy (interferon-β or glatiramer acetate) or (2) switched to dimethyl fumarate (DMF) or teriflunomide (TFL) and compared treatment outcomes using propensity-score-based methods and marginal structural models (MSM).

Results We included 3206 patients in the study. We found no change in risk of 6-month confirmed Expanded Disability Status Scale score worsening in patients switching to DMF (HR: 1.15, 95% CI 0.88 to 1.50) or TFL (HR: 1.16, 95% CI 0.92 to 1.46). The risk of suffering any relapse tended to decrease when switching to DMF (HR: 0.73, 95% CI 0.51 to 1.04) and tended to increase when switching to TFL (HR: 1.25, 95% CI 0.96 to 1.63). Absolute risk differences were small. MSM analyses showed similar results but did not find an increased relapse risk in TFL switchers.

Conclusion Switching from injectable platform therapies to oral first-line therapies in patients with clinically stable RRMS does not increase the risk of disability accumulation. While the postswitch risk of relapses trended towards marginally higher on TFL, this trend was eliminated by adjustment for time-variant confounders.