Which of the following is an oral immunodilator used in the treatment of MS?

Teriflunomide is an oral immunodilator specifically indicated for the treatment of multiple sclerosis (MS). It works by inhibiting the proliferation of T and B lymphocytes, which play a crucial role in the autoimmune process associated with MS. By modulating the immune response, teriflunomide helps to reduce the frequency of relapses and slow the progression of disability in patients with relapsing forms of MS.

In contrast, interferon beta-1b is an injectable medication that belongs to a different class and acts by modulating the immune system but is not administered orally. Edrophonium and pyridostigmine are also not used for MS; rather, they are cholinesterase inhibitors primarily utilized for different conditions, such as myasthenia gravis. Thus, teriflunomide is the only agent among the options that fits the criteria of being an oral immunodilator specifically targeting MS.