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March 7 (Reuters) - The U.S. Food and Drug Administration has called for an assessment of potential neurocognitive side effects of an experimental cholesterol drug being developed by Regeneron and Sanofi, Sanofi said in its annual report on Friday.
The regulatory filing sent shares of Regeneron down 8 percent in Nasdaq trading. U.S.-listed shares of France-based Sanofi were down 1 percent.
The Sanofi statement repeated a filing made by Regeneron last month, in which the company said it had been advised by the FDA that the agency had become aware of neurocognitive adverse events associated with an experimental class of drugs known as PCSK9 inhibitors.
Regeneron and Sanofi are conducting pivotal-stage trials of alirocumab, an PCSK9 antibody designed to block a protein whose natural function is to maintain the presence of "bad" LDL cholesterol in the bloodstream.
The companies said they were not aware of any neurocognitive adverse event signal relating to alirocumab. They also said neurocognitive issues have been associated with the use of statins for lowering LDL cholesterol.
Statins, such as AstraZeneca's Crestor and generic forms of Pfizer's Lipitor, are the most widely used cholesterol-lowering treatments and work by blocking the liver's production of LDL cholesterol.
Both Pfizer and Amgen are also in the late stages of developing PCSK9 drugs.