The present study was a 12-month cohort study to evaluate the efficacy of monthly intravenous (IV) infusion of natalizumab (at a dose of 300 mg) in reduction of relapse rate and expanded disability status scale (EDSS) score of RRMS patients who were referred to Farshchian Hospital, Hamadan, Iran during 2015–2016. The study protocol was approved by the ethical committee of Hamadan University of Medical Sciences. All patients agreed to participate in the study after complete explanations about the study protocol. Written informed consent forms were obtained from all study participants. Samples were selected based on the availability sampling method. Patients were randomly allocated by a medical staff to receive natalizumab (study group, n = 25) or IFN-β (control group, n = 30). Sample size was estimated to be 40 (20 individuals in each group) based on the parameters obtained from Oliveria et al. study [9]:
D = µ1–µ2 = 0.1, α = 0.05, β = 20%, power = 80%, µ1 (relapse rate in study group) = 2.4, µ2 (relapse rate in control group) = 2.5.
Five patients in the study group left the study because of their personal reasons. Demographic data, disease duration, EDSS score and former therapeutic regimens were recorded from all study members. All study participants were diagnosed to have RRMS based on the revised McDonald criteria [10]. The inclusion criteria were age between 18 and 50, two confirmed relapses during the prior year despite IFN-β treatment, appropriate response to high-dose corticosteroid pulse therapy and EDSS score less than 6. Complete blood count (CBC), liver function test, thyroid function test and urine analysis (UA) were tested in all patients. Patients with primary or secondary progressive MS, history of other chronic disorders, cancer, pregnancy, previous administration of cyclophosphamide/mitoxantrone/monoclonal antibodies, chronic liver disease, elevation of liver enzymes/bilirubin/Alkaline phosphatase/Creatinine, white blood cell < 3500 or lymphocyte count < 800 were excluded from the study. Moreover, lack of response to corticosteroid pulse therapy was regarded as an exclusion criterion. Patients in control group received IFN-β [intramuscular injection of 20 μg of CinnoVex (CinnaGen Co, Tehran, Iran) three-times a week] during the study period. Patients visited the clinic every 4 weeks for assessment of the EDSS and any treatment-associated complication. CBC and UA were assessed for patients under treatment with natalizumab in every visit.
Statistical analysis
SPSS version 16 was used for data analysis. Distribution of data was first assessed by the Kolmogorov–Smirnov test. Mean values of relapse rate and EDSS score were compared before and after treatment using paired T test and Wilcoxon test according to the normality of data. Independent T and Mann–Whitney tests were used for comparison of these values between two study groups. Association between categorical variables was evaluated using Chi square test. The relationships between quantitative variables were evaluated using Pearson or ANOVA tests. P values less than 0.05 were considered as significant. EDSS scores in each month were compared using ANOVA test.