FDA staff flag safety fears over Sanofi MS drug Lemtrada


* FDA panel to meet on Nov. 13, FDA verdict due by year-end

* FDA staff cite risk of blood disorders, infections, cancer

* Shares down around 1 percent after the news

By Ben Hirschler and Natalie Huet

Nov 8 (Reuters) - U.S. regulatory officials have raisedconcerns about "multiple serious and potentially fatal safetyissues" in patients given Sanofi's new multiplesclerosis drug Lemtrada, fuelling uncertainty about whether itwill be approved.

Food and Drug Administration (FDA) staff said in a reportprepared ahead of a Nov. 13 advisory panel that the risks mightbe too great to justify approval in the world's biggestpharmaceutical market, unless the drug showed "substantialclinical benefit."

Lemtrada, an injectable treatment also known as alemtuzumab,is one of two new Sanofi drugs for MS, an autoimmune diseasethat attacks the central nervous system and affects more than 2million people worldwide.

The FDA is expected to rule on the drug by the end of theyear. Lemtrada won marketing authorisation from the EuropeanCommission in September, shortly after obtaining approval forits MS pill Aubagio.

The current consensus for annual Lemtrada sales worldwide is$752 million by 2018, according to forecasts compiled by ThomsonReuters Pharma.

Shares in Sanofi fell as much as 2.5 percent after thedocuments were posted on the FDA's website on Friday. By 1555GMT, they had narrowed their loss and were down 0.8 percent at78.01 euros.

"Briefing documents usually raise many questions that areopen for discussion at the upcoming meeting. But when we readthe document it is clearly more negative than usual," aParis-based trader said.


Multiple sclerosis is a chronic, often disabling diseasethat attacks the central nervous system and can lead tonumbness, paralysis and loss of vision.

Lemtrada is given via an intravenous drip for five days andfor three days one year later. It is designed to re-programmethe immune system, but in doing so can make the body morevulnerable to other diseases.

The FDA staff review cited risks of autoimmune diseasesincluding blood disorders, infections and cancer, and, notingthat these issues were "serious and potentially fatal", did notrecommend approval of Lemtrada "unless substantial clinicalbenefit exists".

Natixis analyst Beatrice Muzard said the FDA's notesignalled a greater risk that the drug might not reach the U.S.market.

But another Paris-based analyst, who declined to be named,was less alarmed, pointing out that the side effects cited inthe note were already known.

"Our company is confident that Lemtrada offers an importantstep forward in the way physicians and patients will think abouttreating multiple sclerosis," a spokesman for Sanofi said in anemailed statement.

Sanofi acquired Lemtrada when it bought U.S. biotech firmGenzyme for $20.1 billion in 2011. Lemtrada's prospects were atcentre-stage in that drawn-out takeover battle, leading to aneventual deal that included listed contingent value rights linked to Lemtrada's future success.

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