A revenue loss looms for drugmaker Pfizer as the patent for its hugely popular cholesterol drug Lipitor is set to expire at the end of the year. Lipitor currently accounts for $10 billion in annual sales for the drug giant. And Pfizer isn’t the only pharmaceutical company facing the challenge of expiring patents.

“This is panic time, this is truly panic time for the industry,” said Kenneth Kaitin of the Centre for the Study of Drug Development in an interview with the New York Times.

It is estimated that major drugmakers such as Bayer, GlaxoSmithKline and Novo Nordisk stand to lose $50 billion in revenue this year as other companies rush to replicate their blockbuster drugs. Despite a reported $45 billion in research and development expenditures, strains on big pharma, including a dearth of new drug breakthroughs and price pressure from insurance companies, have curtailed profits.

“I don’t think there’s a company out there that doesn’t realize they don’t have enough products in the pipeline or the portfolio, don’t have enough revenue to sustain their research and development,” Kaitin told The Times.

The economic stresses facing the industry have led to a flurry of corporate mergers in recent years. In 2009, Pfizer bought Wyeth for $68 billion, while Merck purchased Schering-Plough for $41.1 billion. As for Pfizer’s plans, the company has said it plans to invest in some less lucrative medications, such as those that treat cancer and inflammation, in order to remain viable. In addition, over the next two years, Pfizer will reduce R&D funding by 30 percent.