Endo sues Zydus in attempt to block its generic version of Chantix

Since Pfizer’s smoking cessation drug Chantix was recalled in 2021, Endo's subsidiary Par Pharmaceuticals has been the only one to market the product. Now, the generics subsidiary is attempting to ward off fellow generic makers who want in on the drug.

Endo's lawsuit alleges that Zydus launched its Chantix generic, which was FDA approved in June, after Endo alerted it of a new patent but before it could file a patent infringement claim. The new patent covers the method Endo uses to manufacture the drug without the impurities that took down Pfizer's original product. 

Chantix was originally approved in 2006. The drug was flying high with $1.1 billion in peak sales until impurities found in the product brought it crashing down. Pfizer threw in the towel and recalled all lots in September 2021, a month after the FDA cleared Endo's generic ahead of schedule.

Now, the FDA will only accept submissions for products based on Chantix’s active ingredient, varenicline tartrate, if the drugs meet the acceptable intake limit for nitrosamine impurities. That’s what Endo did, where Pfizer and others could not, according to the Aug. 8 lawsuit filed in Delaware federal court.

“Making varenicline tartrate tablets with the low levels of nitrosamine required by the FDA is difficult to do, as evidenced by the fact that Pfizer has been unable to reformulate its Chantix product to meet those requirements despite the huge incentive it has had to do so,” reads the complaint. 

Endo alleges Zydus used the methods listed in its recent patent because those are “the only commercially viable methods” that it’s aware of for ensuring low levels of nitrosamine impurities.

Zydus launched its drug instead of replying to notices sent by Endo, leaving Endo unable to verify if the two companies use the same manufacturing method but finding it "highly likely," according to the complaint. 

It’s likely that Endo can’t afford the generic competition after filing for bankruptcy last August due to the weight of multiple massive opioid-related settlements and $8 billion in debt. The company planned to sell itself to its senior lender group, which would then fund Endo’s opioid settlements.

The U.S. Department of Justice recently shot down that plan on the grounds of bankruptcy law violation because it would pay some creditors while others, including government agencies, would get nothing, Reuters reported.