Drug development for multiple sclerosis (MS), as with any other neurological 
disease, faces numerous challenges, with many drugs failing at various stages of 
development. The disease-modifying therapies (DMTs) first introduced for MS are 
only moderately effective, but given the lack of competition, they have been 
widely accepted in clinical practice. Although safety and efficacy continue to 
be the two main metrics by which drugs will be judged, the newer agents in the 
market also face challenges of a more comparative nature-are they more 
efficacious than the currently available drugs on the market? Are they safer or 
better tolerated? Do they offer any practical advantages over current 
treatments? Fingolimod represented a milestone following its approval as an oral 
drug for MS in 2010, offering patients a far more convenient administration 
route. However, association with cardiovascular complications has led to a more 
cautious approach in its initial prescribing, now requiring cardiac monitoring 
for the first 6 h as well as subsequent monitoring of blood pressure and for 
macular oedema. Natalizumab, amongst licensed drugs, represents the current 
benchmark for efficacy. The risk of progressive multifocal leukoencephalopathy 
during natalizumab treatment is now more quantifiable. Other monoclonal 
antibodies are in various phases of development. Marketing authorisation for 
alemtuzumab has been filed, and whilst trial data suggest that its efficacy 
outperforms both licensed drugs and others in development, there is a 
significant risk of secondary autoimmunity. Its once-yearly administration, 
however, seems particularly advantageous. Rituximab is unlikely to be developed 
further as its license will expire, but ocrelizumab, another monoclonal antibody 
directly targeting B cells, is currently in phase 2 development and looks 
promising. Daclizumab is also moderately efficacious but may struggle to 
establish itself given its monthly subcutaneous dosing. There are new oral drugs 
in development, and it is likely that BG-12 will be licensed this year. This has 
been licensed for psoriasis so there are good safety data in humans that may 
also hold true in MS; however, its three times daily dosage will probably impact 
on patient compliance. Laquinimod has lower efficacy than BG-12 but appears safe 
and could find a place as a first-line agent. Teriflunomide has just been 
licensed by the US FDA and may challenge the current injectable first-line 
therapies as it has a similar efficacy but the advantage of being taken orally. 
However, risk of teratogenicity may caution against its use in some women of 
child-bearing potential. This review will examine drugs that have been recently 
approved as well as those that are in late phase 2 or 3 development as treatment 
for relapsing MS, highlighting their mechanism of action as well as the clinical 
trial and safety data before discussing their potential for success in an 
increasingly florid and complex DMT armamentarium.