Possible Reasons for the Suboptimal Response of the Cladribine Course in Daily Practice: An Independent Analysis of Data from 12 Russian Clinics and the Results of Post-Registration Studies in Other Countries

Objectives: The purpose of this study was to analyze the effect of daily intake of cladribine tablets on the course of multiple sclerosis (MS) while monitoring for 1–4 years during and after the course in several neurological clinics from different regions of the Russian Federation. Materials and Methods: Information was collected on 235 patients from 12 neurological clinics and regional centers for MS, who were observed for an average of 3.4 years after starting treatment with cladribine. Results: An independent analysis of cases of prescription of cladribine in tablets showed that the reason for prescription of cladribine was highly active MS (HAMS) in 159 patients (67.7%), rapidly progressive MS (RPMS) in 20 patients (8.5%), active remitting MS in 50 patients (21.3%) and secondary progressive MS (SPMS) with exacerbations in 6 (2.5%). Among them, only 12 patients (5.1%) had not previously received DMTs, i.e., in these cases, the drug was prescribed as the first DMT. In total, 22 patients had previously received natalizumab, 5—ocrelizumab, and in 1 case—fingolimod. The remaining 207 patients were crossed over from the first-line DMTs. In all cases, there was a decrease in the frequency of exacerbations during and after the completion of the course of cladribine. Exacerbations between the first and second courses of cladribine were noted in 36 patients (15.3% of all treated), almost half of the cases—those who previously received natalizumab (17 exacerbations, or 47.2% of all exacerbations between the 1st and 2nd courses of cladribine), and in 3 cases—from ocrelizumab (in 60% of all patients crossed over from ocrelizumab). During 4 years of follow-up after a full course of cladribine, exacerbations were in 14 patients (6% of all patients included in the analysis), of which in 6 cases—after crossover from natalizumab. Discussion and Conclusions: The data obtained are generally consistent with the results of meta-analyses and reviews published recently, but high probability of exacerbations in patients who were crossed over from second-line drugs such as natalizumab and ocrelizumab were seen. The crossover from natalizumab is carried out more often due to the increased risk of developing progressive multifocal encephalopathy (PML). It is likely that the restoration of MS activity after the withdrawal of natalizumab is quite frequent, cladribine tablets were not able to fully prevent this. Such a crossover does not seem to be optimal, unlike the crossover from first-line DMTs. If such a crossover is still planned, it could be performed within 4 weeks after stopping natalizumab.