Lantus (insulin glargine)
Company: Sanofi
Disease: Type 1 or Type 2 diabetes
Global 2013 sales: $7.9 billion
U.S. patent expiration date: February 2015

Sanofi ($SNY) stands ready to lose exclusivity for its top-selling drug, Lantus, next year. The French drugmaker filed a lawsuit against a biosimilar from Eli Lilly ($LLY) that it expects to tie that up until June 2016 or a favorable ruling for Eli Lilly, whichever comes first.

But Eli Lilly isn't the only threat. Merck ($MRK) is working with Samsung Bioepsis, a joint venture between Samsung and Biogen Idec ($BIIB), to develop a Lantus biosimilar. In August, the FDA gave a tentative approval to Basaglar (insulin glargine injection), the Lantus biosimilar from Lilly and partner Boehringer Ingelheim.

Basaglar has the "same amino acid sequence" as Lantus and is tentatively approved for use with KwikPen, a prefilled dosing device. The FDA cannot give a final approval until the lawsuit is resolved. In June, the EU's Committee for Medicinal Products for Human Use (CHMP) gave a positive recommendation for the approval of Basaglar.

Sanofi is hoping that before that time comes, it will have a successor long-acting insulin. The follow-up long-acting insulin, Toujeo, is under review by the FDA, and Sanofi is hoping for a 2015 launch to get ahead of a Lantus biosimilar. The pharma already offers deep discounts in Europe for Lantus, so there's not much of a price difference compared to a biosimilar, nor much incentive to switch. But losing U.S. Lantus sales would really hurt--last year that drug accounted for more than one-third of Sanofi's operating profit.

Then-CEO Chris Viehbacher said of Toujeo on Sanofi's 2Q14 earnings call, "This is a medicine that offers the efficacy and the confidence and safety of Lantus while offering lower hypoglycemia--glycemic events."

Last year, Lantus had $7.9 billion in global sales; that was 17.3% of the company's revenues and the top-selling Sanofi diabetes product.

For more:
Can Sanofi parlay low Lantus prices into Toujeo sales? That's the billion-dollar question
Lilly and Boehringer snag EU nod for Lantus knockoff, but stateside hopes stay on ice
Lilly grabs a 'tentative' FDA OK for insulin treatment, but Sanofi still blocks its path
Is a price war imminent when Sanofi's Lantus patent falls?
Sanofi's Lantus empire imperiled as EU recommends Lilly, Boehringer biosimilar
Merck takes aim at Sanofi with a Lantus biosimilar of its own
Sanofi wards off Lilly's Lantus challenger with infringement lawsuit
Sanofi has Lantus for now but says its successor is looking good

-- Stacy Lawrence (email | Twitter)