Multiple sclerosis is unique among neurological diseases in that there are currently eight treatments for this one condition that have received approval by the U.S. Food and Drug Administration (FDA). Five of these drugs require subcutaneous or intramuscular injection, two are administered intravenously, and fingolimod, the newest agent on the block, is given orally. None are considered curative, but these disease-modifying therapies (DMT) have led to a reduction in relapse rates and the progression of disability.
Despite this progress, each of the drugs comes with side effects, including flu-like symptoms with the interferons, lipoatrophy with glatiramer, progressive multifocal leukodystrophy (PML) with natalizumab, and congestive heart failure or leukemia with mitoxantrone. As the first oral agent for MS, fingolimod created great expectations prior to FDA approval. Its popularity, however, has been surprisingly limited, presumably due to the potential for unknown long-term risks. The occur rence of PML with natalizumab demonstrated to MS neurologists and patients the potential risks associated with new drugs.
Additional DMTs in the pipeline may increase MS-management effectiveness in coming years, although safety will continue to be a major consideration in the use of these drugs. For instance, oral cladribine was on the verge of FDA approval in early March when the agency referred the drug back for more safety studies. This drug is already used in intravenous form for the management of hairy cell leukemia, but it is being studied for use with remitting relapsing MS because of its apoptotic effects on lymphocytes. If cladribine is ultimately approved for use, the risk of infection and neoplasms may limit its use.
Other oral agents being studied include: