Which drug is noted for being a potent immunosuppressant that reduces relapse rates in MS?

The drug noted for being a potent immunosuppressant that reduces relapse rates in multiple sclerosis (MS) is indeed Mitoxantrone. This drug works by interfering with the DNA synthesis and function, which ultimately leads to the inhibition of activated T and B lymphocytes, thus reducing the autoimmune response characteristic of MS. Mitoxantrone is particularly effective in patients with aggressive forms of the disease, and its immunosuppressive properties help in decreasing the frequency of relapses.

While Alemtuzumab is also an immunosuppressant used in MS treatment, it primarily functions by depleting lymphocytes through a different mechanism, making it effective in patients with specific types of MS as well. Diethyl fumarate is a therapeutic option that primarily acts by activating the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway, which is more focused on neuroprotection rather than direct immunosuppression. Pseudoparkinsonism, on the other hand, is not applicable in this context as it depicts a side effect rather than a drug treatment.