Endo International sues Zydus Pharma to block generic version of Pfizer Chantix

Endo's generic drugmaking subsidiary Par Pharmaceutical said in a complaint made public on Wednesday that Zydus' generic infringes a newly issued U.S. patent covering Endo's process for making its version of the drug.

Endo received the patent on Tuesday, covering a method of manufacturing Chantix's active ingredient varenicline with safe levels of the impurities that caused Pfizer to take Chantix off the market. Endo asked the court to block Zydus' U.S. sales of its generic and requested an unspecified amount of money damages.

Representatives for Endo, Zydus and Pfizer did not immediately respond to requests for comment on Wednesday.

Chantix earned Pfizer more than $1 billion in sales in 2019. Pfizer recalled the drug in 2021 after finding it contained high levels of impurities that increase cancer risks.

Endo launched a generic version of the anti-smoking drug with fewer impurities later that year.

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It said making the FDA-approved tablets 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.

The FDA approved India-based Zydus' generic-drug application for its version of Chantix in June. Endo said Zydus has since launched the generic in the United States.

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The case is Par Pharmaceutical Inc v. Zydus Pharmaceuticals (USA) Inc, U.S. District Court for the District of Delaware, No. 1:23-cv-00866.

For Endo: Martin Black of Dechert

For Zydus: Not yet available

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