Facing a dearth of new multi-billion dollar “wonder drugs,” the big global pharmaceutical companies are desperate to keep generic drug makers away while they try to squeeze every last dollar out of their precious patents.

“Ninety percent of big pharma’s revenues are going to fall of the face of the planet in three years,” said Dr. Bijan Salehizadeh, a partner with venture capital firm Highland Capital Partners, which invests in early-stage drug makers.

The revenues are disappearing because the big pharmaceutical companies have struggled to develop new drugs that appeal to vast numbers of patients. Moreover, the biggest money-making drugs in their portfolios are soon going off patent, leaving them open to competition from equally effective generic drugs that cost a fraction of their brand-name counterparts. 

According to the Wall Street Journal, the largest drug companies are expected to lose $67 billion in profits to generics between 2008 and 2012.

Consider Pfizer’s blockbuster cholesterol drug Lipitor, which had $12.7 billion in sales just last year and generates about 25% of Pfizer’s annual revenue.

Pfizer got a little breathing room last week when it settled a five-year patent dispute with Indian drug maker Ranbaxy Laboratories. Originally, a generic version of Lipitor was expected to hit the market by March 2010. But the agreement between Pfizer and Ranbaxy will postpone any generic competition until November 2011.

“This agreement is a win-win-win because it is pro-patient, pro-competition and pro-intellectual property,” said Ian Read, president of Worldwide Pharmaceutical Operations with Pfizer. “It provides certainty regarding the timing of the entry of a generic version of Lipitor.”

More importantly, it could provide an additional $5 billion-worth of revenue to Pfizer’s bottom line, according to Bank of America analysts.

Settlements with generic companies are an effective method for the makers of brand name drugs for extending the shelf life of the blockbuster products. In 2006, Bristol-Myers Squibb Co. (BMY) worked with a Canada-based generic drug maker to keep its blood thinner Plavix from going generic until 2011.

Some drug makers have taken to buying up the generic drug companies. In 2005, Novartis purchased the generic drug maker Eon Labs and merged it into the company’s main business – allowing the generic and brand name drugs to be made by the same company.

“Novartis is now vertically playing the entire pharmaceutical industry across the whole value chain,” Mark Bard, president of Manhattan Research.

Big Pharma is also pushing through what’s known in the industry as “lightly-branded generics.” The most recent example is Pfizer’s generic version of the company’s anti-depressant Zoloft, which the company issued in 2006 after the drug went off patent..

Despite these efforts to stave off competition, experts say the pharmaceutical companies are doing whatever they can to wring whatever profits are left in their branded drugs.

“There’s a huge amount of uncertainty in the market right now for the big pharmaceutical companies,” said Dr. Kevin Schulman, director of Duke University’s Fuqua School of Business health care management program. “But right now, this is a great time for the generics.

The big generic companies Teva (TEVA) have issues, as well. With no blockbuster drugs in big pharma’s pipelines, the generic companies don’t have anything to copy. So while consumers may benefit from the sharp decline when a drug goes off patent, at some point generic drug companies will face a price war among themselves, which will cannibalize their own profits.

“There isn’t another Lipitor or Viagra waiting in the wings right now,” Salehizadeh said. “The era of the broadly-marketed big-name drug is over.”