3. Chantix

Pfizer building
The basic patent for Pfizer's Chantix expires in late 2020. (Tracy Staton)

Use: smoking cessation 
2019 U.S. sales: $899 million 
Main patent expiration: November 2020 

Pfizer has dealt with some costly patent expirations in recent years for Viagra and Lyrica, and the company expects the erosion to continue this year. It's projecting a $2.4 billion hit to 2020 sales from generics and biosimilars.

Chantix, which is used to help smokers quit, may well contribute to those losses by year's end. It’ll lose its main patent in November, but other patents stretch to 2022, so it remains to be seen exactly when generics will launch. The drug generated $899 million in the U.S. in 2019.

Par Pharmaceutical acquired a generic from Actavis and later sued Pfizer seeking a declaration from the court that its generic version wouldn’t infringe Pfizer’s 2022 patents, court records show. Par didn’t challenge the November 2020 patent. 

In its lawsuit, Par said Pfizer didn’t respond within a 45-day deadline to assert its patent claims after Actavis applied for approval to market the generic. Par later withdrew its suit, and court filings didn’t say what had happened. Endo, which owns Par, didn't respond to a request for comment.

A Pfizer spokesman said the company "does not speculate if or when a generic company will launch a generic version of Chantix."

Chantix won original U.S. approval in 2006, and as the drug nears the end of its exclusivity, its price has grown significantly. In 2018, GoodRx reported that Chantix’s price had doubled over the last 5 years. 

RELATED: Price of Pfizer's smoking-cessation drug Chantix doubles in just 5 years: report 

Whenever Chantix loses exclusivity, it’s set to follow other declines by other big Pfizer brands such as Viagra and Lyrica. Still, the company believes it's nearing an end to its recent streak of patent expirations. 

Overall, Pfizer said in an annual filing it expects the “impact of reduced revenues due to patent expiries will be significant in 2020, then moderating downward to a much lower level from 2021 through 2025."

3. Chantix