Sanofi has previously filed patent infringement suits against other rivals, including Merck and Co and Eli Lilly & Co, to block cheaper versions of the diabetes drug from coming to the market.

The company is heavily reliant on Lantus, its leading product with sales of 4.62 billion euros ($5.26 billion) in 2017.

Sanofi's Paris-listed shares fell 1 percent. The company declined to comment.

Lantus is a long-acting insulin used to treat adults with type 2 diabetes and adults and pediatric patients with type 1 diabetes to control high blood sugar.

Sanofi, which settled with Lilly allowing it to launch Basaglar, an insulin similar to Lantus in 2016, sued Mylan in October 2017.

The case includes some patents covering a disposable injection pen version, Lantus SoloSTAR. That litigation is pending and no trial date has been set, Mylan said.

Mylan's generic versions of Lantus and Lantus SoloSTAR, developed with India's Biocon, are being reviewed by the US Food and Drug Administration.