Sanofi group Genyme is not taking the decision by US regulators to reject its multiple sclerosis drug Lemtrada (alemtuzumab) lying down.

The company said it "strongly disagrees" with the US Food and Drug Administration's stance that clinical trial data submitted for the drug is lacking, and that it will appeal the decision.

The agency has issued a Complete Response Letter for Lemtrada basically asserting that Genzyme has failed to submit evidence showing that its benefits outweigh its serious adverse effects. 

In addition, to have a hope of getting its drug onto the all-important US market, Genzyme must carry out additional active comparator studies of different design and execution to those submitted, it said.

But Genzyme president and chief executive David Meeker insists that the existing clinical trial programme for Lemtrada "provides robust evidence of efficacy and a favourable benefit-risk profile," and also points out that it formed the basis for regulatory green lights around the world thus far. 

The drug has been approved in Europe, but its failure in the US market will no doubt substantially trim sales forecasts (previously around the $700 million mark by 2018, according to forecasts compiled by Thomson Reuters), and Sanofi will now have to make the decision whether it will be worth undertaking further expensive studies.