(Reuters) - French drugmaker Sanofi sued Eli Lilly and Co on Thursday, alleging that the U.S. pharmaceutical company infringed patents on its top-selling diabetes treatment, the insulin product Lantus.
The lawsuit, filed in United States District Court for the District of Delaware, was triggered by notification from Lilly last month that it applied with the U.S. Food and Drug Administration (FDA) seeking permission to sell a generic version of Lantus, known chemically as insulin glargine.
Lilly, in its submission, challenged the validity of several patents on Lantus held by Sanofi.
Lantus is the world's most prescribed insulin product, with annual worldwide sales of about $7 billion.
Indianapolis-based Lilly had said it will not launch its generic product before the February 2015 expiration of Sanofi's patent on the active ingredient in Lantus.
But the patent infringement lawsuit triggers an automatic 30-month stay of a generic approval by the FDA, which would keep Lilly's generic off the market until mid-2016.
Sanford Bernstein analyst Tim Anderson, in a recent research note, said a 30-month delay would raise Sanofi's earnings per share from 2015 through 2020 by about 6 percent and lower Lilly's EPS for the period by about 2 percent.
A delay in the launch of a generic by Eli Lilly would also give Sanofi more time to switch patients to a new long-acting follow-up product known as U300 once it gains approval before cheap competition for Lantus hits the market.
(Reporting by Bill Berkrot; Editing by Amanda Kwan)