Background and importance Currently, there are many approved disease-modifying treatments (DMTs) for the management of multiple sclerosis (MS) with variable potencies (first-line and second-line therapies), different schedules, mechanism of action, route of administration and side effect profile. None of them are curative. Modification between first-line DMTs or switching to second-line are proposed when the disease progresses, and no universal guidelines exist for switching therapies.

Aim and objectives To describe the reasons that brought about treatment modification in routine clinical practice with reference to: switch, temporary interruption or permanent discontinuation.

Material and methods During the retrospective study period (December 2019–December 2020) patients with relapsing MS were analysed.

Collected data were: age, sex, DMT before and after switch, reason for treatment modification, duration of initial therapy, number of changes.

Results Of 200 analysed patients, 106 had treatment modification, 69 were women, mean (SD) age was 39.9 (9.47) years.

82 patients had received one previous treatment with median duration 58 months, and 24 received at least two treatments.

8 patients had temporary interruptions (4 for pregnancy and 4 for other personal reasons) and none had permanent discontinuation. The main drugs used before the modification were the interferons IFNb-1a (50%) and IFN-1b (38%), and after the modification teriflunomide (33%) and natalizumab (44%). Reasons for treatment switch were unacceptable breakthrough disease activity (60 patients), treatment intolerance (35 patients) and JC virus (JCV) activation with progressive multifocal leukoencephalopathy risk (11 patients).

Of the patients with a suboptimal response, unfortunately 9 patients with duration of treatment more than 20 years converted to secondary progressive MS with permanent disability.

Regarding treatment intolerance, the most remarkable reasons were IFN-related flu-like symptoms, depression and injection site reactions.

Conclusion and relevance Modification between first-line DMT or escalation to higher potency therapies was a common occurrence during our study. Most patients were treated with first-line drugs before and after the modifications.

Lack of efficacy remains the main driving force behind switching. These results confirmed that some patients can experience disease activity despite injectable or oral DMTs, which necessitates escalating to a more potent treatment for preventing worsening of disability. Determining which DMT is best for which patient and when to switch remains a major challenge, and the patient’s personal preferences should be considered.

Conflict of interest No conflict of interest