I wonder whether someone at Bayer just found an old box of patent documents tucked in the corner of an office that hasn't been used in years.

The drugmaker is suing Abbott Labs (NYSE:ABT), claiming that Abbott's TNF-inhibitor Humira infringes on one of Bayer's patents.

One has to wonder what took Bayer so long to file the lawsuit. The patent was issued in 1997, and Humira has been on the market for more than six years now. Maybe no one at Bayer noticed that the company owned the patent, but it seems just as likely that the drugmaker was waiting to see how large revenues from the drug could get before filing the infringement lawsuit. If the lawsuit is a shot in the dark, it might make sense to pay for the lawyers only if the long-shot potential royalty stream justifies the cost. And it just might pay off, if the company can get a cut of $4.4 billion, the drug's 2008 sales figure.

The anti-TNF market seems to be filled with patent infringement lawsuits -- not surprising, considering that the class of drugs brought in more than $11 billion cumulatively last year. Johnson & Johnson (NYSE:JNJ), which, alongside Schering-Plough (NYSE:SGP), sells Remicade, another anti-TNF drug, is also suing Abbott. J&J claims that Humira violates patents it owns, according to The Associated Press. And earlier this year, Ariad Pharmaceuticals (NASDAQ:ARIA) was on the losing end of its lawsuit claiming that Amgen (NASDAQ:AMGN) and Wyeth's (NYSE:WYE) anti-TNF compound, Enbrel, infringed on patents that Ariad had licensed from three academic institutions.

Unless you're a patent attorney -- and perhaps even if you are -- it's rather difficult to figure out the chances that the companies will win these lawsuits. The best investors can do is hope that the companies they own hire good lawyers who can turn the tide in their favor. 

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.