A study published today in the New England Journal of Medicine shows that a drug combination being developed by Gilead Sciences works better and has fewer side effects than a GSK drug that has been a backbone of AIDS treatment.

The study, sponsored by Gilead, is fueling a battle that has been in the making since the California-based Gilead bought Triangle Pharmaceuticals of Durham three years ago.

The acquisition allowed Gilead, which employs about 120 in Durham, to challenge GSK, which has a U.S. headquarters in Research Triangle Park. The British pharmaceutical giant's AIDS drug research and development is based in the Triangle.

The study results bolster Gilead's efforts to reduce to one a day the number of pills patients infected with the AIDS virus would have to take. The pill, which would include a drug developed by Triangle Pharmaceuticals, could become available in less than a year. Gilead is planning to ask for regulatory approval of the drug this summer.

"If everything goes well for Gilead, it'll be a bruise for GSK," said Zach Wagner, an Edward Jones analyst who tracks the pharmaceutical industry.

"GSK is considered a leader" in AIDS drugs on the market, Wagner said. "Where they're lacking is in the [drug development] pipeline. I believe there's a lot going on in the labs. They just don't have much to show for it."

GSK doesn't have anything new on hand to compete with Gilead's three-in-one combination pill. Instead, the drug maker is counting on physicians' familiarity with its two-in-one combination pill Combivir.

In a statement, GSK said that Combivir has been evaluated in more than 50 studies involving more than 18,000 patients, and is found to be effective and safe. "We are always interested in learning more about existing treatments for HIV, but we realize the limited value of a single, open-label study to make comparisons among products," Mark Shaefer, who heads GSK's HIV drug development, said in the statement. In an open-label study, patients know which drugs they are taking.

But patients infected with the human immunodeficiency virus, the virus that causes AIDS, have been waiting for a potent three-in-one pill for about a decade. HIV/AIDS experts at Duke University and the University of North Carolina at Chapel Hill called it the holy grail of AIDS drug treatment. They expect that most newly diagnosed patients would be prescribed Gilead's three-in-one combination rather than a combination including Combivir, GSK's staple treatment.

For the past eight years, physicians have relied heavily on a combination of Combivir and Sustiva, a Bristol-Myers Squibb drug. Combivir is a combination of AZT, the AIDS drug developed by GSK's predecessor Burroughs Wellcome, and an antiviral drug called Epivir.

Side effects caused by AZT, such as anemia and fatigue, have caused physicians and patients to look for an alternative to Combivir.

Gilead provided that alternative in August when it brought Truvada to market. The pill combines two medications, Gilead's Viread and Triangle Pharmaceuticals' Emtriva.

Truvada "has captured a major part of the market, because it addresses the shortcomings of AZT," said Dr. Charles Hicks, an HIV/AIDS expert at Duke University.

Truvada sales in the United States have soared in the past 18 months, while U.S. sales of Combivir have declined, analysts said. The companies' 2005 sales figures have not been released.

The study that appears today in the New England Journal of Medicine compares a regimen of Sustiva and Gilead drugs Viread and Emtriva to a Combivir-Sustiva regimen. It found that Gilead's three-way combination is not only more effective against the AIDS virus, but also causes fewer side effects. The study, which included 517 newly diagnosed patients, was started before Truvada received regulatory approval.

"We had momentum before," said Norbert Bischofberger, Gilead's head of research and development. "Publication of the study results will accelerate this trend."

Gilead could not have challenged GSK without the help of Triangle Pharmaceuticals, Bischofberger said. Adding Triangle Pharmaceuticals' laboratories in Durham was nice, he said.

"But I can tell you now that the real justification for buying Triangle was emtricitabine," Bischofberger said, referring to the chemical name of Emtriva.

Last year, chemists at Gilead's California operations figured out how to layer the three-in-one combination pill. But scientists in Durham analyzed all the pill samples used in tests with patients.

"Those people in Durham worked over Thanksgiving and Christmas," Bischofberger said. "It was remarkable."