German neurologists are standing by currently prescribed interferon-based multiple sclerosis treatments, despite a warning issued by the Federal Institute for Drugs and Medical Devices, BfArM.

The Bonn-based agency has informed prescribing physicians that five of the drugs, including Bayer's Betaferon/Betaseron, Merck KGaA's Rebif, Novartis' Extavia and the Plegridy and Avonex treatments supplied by US biotechnology firm Biogen Idec, could touch off a rare thrombotic microangiopathy characterized by hypertension, fever and severe liver damage.

Medical practitioners have said they believe the threat is not significant enough to withhold products that have been successfully employed for more than 20 years; however, they intend to carefully monitor patients for danger signs.

The physicians' view is also backed by the German Multiple Sclerosis Society, DMSG. The society represents the interests of German MS patients, believed to number around 130,000.

Betaferon/Betaseron was Bayer HealthCare's top-selling drug in 2013, with sales of just over €1 billion. Rebif was also Merck's top seller, bringing in 2013 revenue of €1.86 billion.