Earlier in the week, small biopharma Trimeris (NASDAQ:TRMS) revealed that it and partner Roche were being sued for patent infringement by Novartis (NYSE:NVS) over Trimeris' only marketed compound, Fuzeon.

Fuzeon, an HIV therapy, is approved in the U.S. and the European Union, among other places. Trimeris' development partner, Roche, helps market the first-in-class fusion inhibitor; sales of the drug were $200 million worldwide in the first nine months of 2007.

The Novartis lawsuit claims that Trimeris and Roche are infringing on a patent that Novartis was recently granted, but which it applied for all the way back in 1995 -- before Fuzeon's 2003 FDA approval date. Trimeris was light on the details about the lawsuit in the regulatory filing (seen here), because it hasn't been formally served yet.

Regardless of whether the Novartis suit has merit, racking up millions of dollars in legal fees fighting a patent suit is the exact opposite of what Trimeris needs right now. If Roche doesn't cover most of the costs of the lawsuit, then Trimeris' slim $16.9 million operating margin (in the first nine months of this year) will vanish to the lawyers.

Recently, Trimeris has been suffering from competitive woes in the U.S., as Pfizer's (NYSE:PFE) recently approved HIV therapy Selzentry, and soon Merck's (NYSE:MRK) Isentress, will bite into sales of Fuzeon. Sales of Fuzeon were down 8.9% year over year in the U.S. and Canada this quarter, even with only a few months of Selzentry competition. Still, international sales growth of Fuzeon has remained strong.

It's a bit ironic to see Novartis essentially suing itself, considering that it owns 33.3% of the voting rights in Roche and 6.3% of all outstanding Roche equity. Even if Trimeris loses the suit, there is almost no chance that it will have to give up all Fuzeon revenue. But the possibility of having to turn a chunk of revenues over to Novartis as royalties, even a single-digit percentage, would meaningfully affect Trimeris' already slim profits.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. Pfizer is an active Inside Value pick. The Fool has an A+ disclosure policy.