GlaxoSmithKline (NYSE: GSK) is moving to protect its top selling HIV drug Epzicom from generic drug competition.

ViiV Healthcare, the HIV joint venture of GSK and Pfizer (NYSE: PFE) is suing Teva Pharmaceutical (Nasdaq: TEVA) for infringing on HIV drug Epzicom in violation of the drug’s patent, Bloomberg News reports. The Aug. 5 complaint was filed in federal court in Wilmington, Del.

ViiV was formed in 2009 to market HIV drugs and develop new HIV treatments. The company is based in London with U.S. headquarters at GSK’s campus in Research Triangle Park. ViiV’s portfolio of 10 HIV drugs generated 2010 sales topping $2.4 billion. Epzicom generated $860 million in total 2010 sales for ViiV, according to GSK filings; $325 million in U.S. sales. It is ViiV’s top selling HIV drug.

GSK gained Food and Drug Administration approval on Epzicon in 2004. The combination drug pairs antiretroviral drugs abacavir and lamivudine in one pill. Epzicom’s patent expires in 2016. GSK said in court documents that Teva’s application to sell generic Epzicom tablets infringes on the drug’s 2002 patent.

Another ViiV product, Combivir, is also under threat of generic competition from Teva. Teva in May received Food and Drug Administration approval on its application to market a generic version of combivir. Combivir is a combination drug that pairs azidothymidine, also known as AZT, with antiviral lamivudine. The drug, approved in 1997, was the first combination therapy made available for HIV-infected patients.

Combivir generated $563 million in total 2010 sales; $222 million in the United States. Teva expects its generic Combivir will become available in the fourth quarter under a settlement with GSK and ViiV.

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