US and European regulators approved Biogen Idec's dimethyl fumarate (BG-12) for the treatment of relapsing–remitting multiple sclerosis (RRMS), setting the stage for an MS market reshuffle and blockbuster expectations.

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The lowdown: Dimethyl fumarate is an immunomodulatory small molecule with a mass of just 144 g per mol. Although its mechanism of action is unknown, it has been shown to activate the NRF2 (also known as NFE2L2) antioxidant response pathway. First used medically in the 1950s as a treatment for psoriasis, Fumapharm and Biogen Idec started working on the drug together for MS in 2003. (Dimethyl fumarate was also until recently used to prevent mould from growing in furniture.)

Two pivotal trials of the oral drug in around 2,000 patients both met their primary end points. In one, the drug nearly halved the number of patients who had relapsed at 2 years when compared to placebo (27% versus 46%). In the second, the drug nearly halved the annualized relapse rate versus placebo (0.224 versus 0.401). Adverse effects noted in the trials included reductions in white blood cell counts, flushing, nausea, vomiting and diarrhoea. Based on the promising efficacy, relatively clean safety profile and oral delivery, many analysts expect the drug to displace much of its disease-modifying competition, which includes interferon betas, Teva's glatiramer acetate, Biogen Idec's natalizumab and Novartis's fingolimod, the first oral disease-modifying MS drug to make it to the market.

BioMed Tracker forecasts annual worldwide sales of US$5.7 billion for dimethyl fumarate by 2018. Biogen Idec has priced the drug at just under $55,000 per year, a discount of around 9% from fingolimod.