Piper Jaffray analyst Edward Tenthoff attributes the weakness in shares of Regeneron Pharmaceuticals (REGN) to the FDA alerting Sanofi (SNY) of fill-finish manufacturing deficiencies for certain products including sarilumab.

Sarilumab is an IL-6 antibody for the treatment of rheumatoid arthritis with an October 30 FDA action date and is manufactured at Regeneron's antibody manufacturing facility in Rensselaer, New York, Tenthoff tells investors in a research note.

The analyst points out that Regeneron reports Q3 results on November 4 and that he expects EYLEA sales of $835M. He maintains a Neutral rating on the shares with a $447 price target.

Regeneron is trading down 3%, or $9.90, to $355.45 in early trading.