5. Xolair

Roche recorded $1.83 billion in U.S. Xolair sales last year. (Image: Roche)

Company: Roche/Novartis 
2017 U.S. sales: $1.83 billion 
Disease: Allergic asthma and chronic idiopathic urticaria 
Patent expiration: 2018 

First approved in 2003, Novartis and Roche's Xolair has grown to provide a reliable revenue stream, representing blockbuster sales for Roche and nearing that amount for Novartis. 

But while a key patent expires in 2018, it's unclear when any biosimilars could challenge the drug which treats allergic asthma in patients 6 and older and chronic idiopathic urticaria in patients 12 and older.  According to the Generics and Biosimilars Initiative, Glenmark and Sorrento have biosimilars in development, but neither has submitted their programs for FDA approval. 

Glenmark only won the FDA's blessing to start human trials last year, so that company's program has a ways to go before a potential launch. Sorrento's partner MabTech completed a phase 2 and 3 study in China in 2016, but Sorrento hasn't detailed plans to advance the program in the U.S. A Sorrento spokesperson declined to provide further details.

In its annual report, Novartis notes that the drug's compound patent expires this year, while other syringe formulation patents expire in 2021 and 2024. 

RELATED: Glaxo aims to lure patients from Novartis' Xolair with Nucala switching study 

Roche, which records U.S. sales for the med, didn't list the the allergic asthma and chronic idiopathic urticaria med as potentially facing competition this year on its annual SEC filing. The company recorded Xolair sales that were up 16% for the year to CHF 1.74 billion ($1.83 billion) due to more uptake.

For its part, Novartis recorded $920 million in Xolair sales under a U.S. profit-sharing arrangement with Roche, plus ex-U.S. sales. 

Novartis is also testing the drug to treat nasal polyps, an indication that could be ready for filing in 2020. It's currently in phase 3 testing in that use. 

5. Xolair