LONDON (Reuters) -Shares in French drugmaker Sanofi fell more than 9% on Thursday after late-stage trial data for its experimental inflammatory disease drug amlitelimab fell short of Wall Street expectations.

Sanofi has been developing amlitelimab for atopic dermatitis, a severe form of eczema. Its blockbuster medicine Dupixent treats the same skin condition, and Sanofi hopes its new drug could complement or eventually succeed it. Dupixent is set to lose patent protection in 2031.

Analysts at Jefferies said the Phase III results for the drug for treatment of atopic dermatitis fell short of its earlier trial and looked weak against rival biologics drugs, though the drug's safety profile and convenient 12-week dosing could still support its use.

JPMorgan analysts noted that the data shows that amlitelimab is less effective than Dupixent.

Shares were down 8.9% at 0807 GMT, making Sanofi the biggest faller on Europe's blue-chip STOXX 600 index.