Sanofi is heavily reliant on Lantus, its leading product with sales of 4.62 billion euros ($5.26 billion) in 2017, and Mylan's own insulin drug would be its second competitor after Eli Lilly launched its version in late 2016.
Shares in Sanofi, whose diabetes revenues have fallen since 2015, as Lantus is squeezed by pricing pressure, fell 1 percent on the Mylan announcement, although the French group said its U.S. rival would not be able to launch its insulin drug.
"We believe that it is unlikely that the Patent Trial and Appeal Board (PTAB) ruling on the formulation patents will have an impact on Mylan's timing for a launch of its glargine products," a Sanofi spokesman said in an emailed statement.
"The PTAB decision alone does not affect the existing 30-month stay and Mylan does not have tentative Food and Drug Administration approval for its products at this time."
Mylan was not immediately available for comment.
The 2017 case, which includes some patents covering a disposable injection pen version, Lantus SoloSTAR, is pending and no trial date has been set, Mylan said.
Separately, Mylan's generic versions of Lantus and Lantus SoloSTAR, developed with India's Biocon, are being reviewed by the FDA.
($1 = 0.8786 euros)
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