Sanofi's MS drug Lemtrada tripped up again, this time in U.K.

Less than a month ago, Sanofi's ($SNY) multiple sclerosis treatment Lemtrada ran into problems with FDA staffers who were unconvinced of the drug's safety and efficacy. Now, it looks as if the U.K. may share some of those doubts. Its cost-effectiveness gatekeeper has asked the French pharma for more data, giving the company just over a month to submit the supplementary information.

According to Bloomberg, the National Institute for Health and Care Excellence (NICE), which advises Britain's National Health Service, needs some clarification on the evidence submitted by Sanofi's Genzyme unit. And while NICE didn't make public what information it's after, last month's FDA review offers a few clues.

"Serious and potentially fatal safety issues" was the phrase the FDA delivered to Sanofi in November, putting a major dent in its hopes for approval in what would make up its most lucrative market. But concerns didn't end there. MS patients--and regulators--sometimes show willingness to overlook safety flags in search of effective treatment, as they've done with competitors Tysabri from Biogen Idec ($BIIB) and Gilenya from Novartis ($NVS). But reviewers questioned whether the trials Sanofi conducted actually proved a substantial clinical benefit for its contender.

As one analyst put it, the combination of safety and efficacy worries is "like a death sentence" for Lemtrada, and a setback in the U.K. certainly wouldn't help. The EU approved the drug in September, and analysts estimate it could rack up sales of €455 million ($619 million) in 2017. Sanofi has been counting on sales of the drug, which played an important role in the company's $20 billion pickup of Massachusetts-based Genzyme in 2011, to help it regroup after the patent cliff claimed products like blockbuster Plavix.

But NICE's recommendations often set precedents for other governments making value decisions, and those could take on increasing importance as the MS drug landscape crowds. In addition to injectable competitors like Tysabri and Teva's ($TEVA) Copaxone, the FDA has also approved some oral MS alternatives, including the hot seller Tecfidera from Biogen and Sanofi's own pill, Aubagio.

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