The goal of this clinical trial is to determine whether treatment with indapamide can slow the rate of progression in patients with progressive forms of multiple sclerosis (MS). The main question it aims to answer is whether this treatment can reduce the speed at which the walking speed of patients with progressive MS (PMS) worsens. Participants will take an indapamide tablet once daily for 12 months. During this time, among others, their walking speed will be assessed several times.