This study was aimed to describe changes of Disease-Modifying Treatments (DMT) in an Italian cohort of patients with multiple sclerosis (MS) and to identify predictors of therapeutic modifications. Patients with MS and treated with the first-line injectable DMT (interferons-IFNs or glatiramer) between 1/7/2009 and 31/10/2012 were selected from administrative databases of the MS Center of Cagliari (Sardinia, Italy). Socio-demographic, therapeutic, and clinical information was collected in the 6 months preceding the index date. All patients were followed for 36 months to evaluate therapeutic changes in terms of non-adherence, switch, temporary discontinuation, and permanent interruption. Predictors of changes were estimated by multivariable regression models. Data on 1698 patients were collected: glatiramer was prescribed in 27% of cases, IFN beta-1b in 22%, IFN beta-1a-im in 20%, IFN beta-1a-sc-44mcg in 19%, and IFN beta-1a-sc-22mcg in 12%. Non-adherence was observed in 25% of cases, therapeutic switch in 30%, discontinuation in 37%, and permanent interruption in 28%. The risk of non-adherence was higher for IFN beta-1b, compared with IFN beta-1a-im (adjOR = 1.73). Therapeutic switch occurred especially in patients recently diagnosed (each year from diagnosis causes a decrease of this risk adjHR = 0.97); the risk of discontinuation was higher with EDSS = 4-6 and 7-9 (adjHR = 1.52 and 4.42, respectively). The risk of permanent interruption increased with the augmentation of disability (adjHR = 1.67 and 5.43 for EDSS 4-6 and 7-9). This study mirrored a detailed framework of DMT prescription and identified factors related to changes in the MS therapy. These findings could support healthcare providers in the evaluation and maximization of benefits associated with a long-term DMT.