Natalizumab treatment of multiple sclerosis in Spain: Results of an extensive observational study

Natalizumab has been shown to be effective in pivotal clinical trials in multiple sclerosis; however, the patients in whom treatment is indicated in clinical practice have a different clinical profile from those included in the clinical trials. The aim of this study is therefore to collect data on natalizumab use in everyday clinical practice in Spain. The 86 participating centers throughout Spain submitted data on disease characteristics at baseline and after treatment. Valid data were available for 1,364 patients (69.3% women, 86.9% with relapsing-remitting disease). Ninety-three percent had received prior therapy for multiple sclerosis. For the 825 patients on treatment for at least a year, the annualized relapse rate (ARR) decreased from median 2.0 [mean 2.01, 95% confidence interval (CI) 1.92-2.11] in the year prior to natalizumab to 0.0 (mean 0.25, 95% CI 0.21-0.29) at 1 year (p<0.001). The Expanded Disability Status Scale (EDSS) score decreased from median 3.5 at baseline (mean 3.71, 95% CI 3.60-3.82) to 3.0 (mean 3.37, 95% CI 3.25-3.49) (p<0.0001). The discontinuation rate was 14%. One patient discontinued natalizumab due to progressive multifocal leukoencephalopathy (PML) and another due to probable PML (subsequently confirmed). Although our patients had more severe disease than those in the pivotal study, a similar reduction in ARR was observed. This finding is in line with previous observational studies. The effect was independent of baseline EDSS.