July 24 (HealthDay News) -- New research offers more evidence that a new AIDS drug brings significant benefits to patients who have failed other treatments.

The drug, known as raltegravir (Isentress), almost doubles the likelihood that patients will beat back the AIDS virus despite being immune to other medications, according to a study in the July 24 issue of the New England Journal of Medicine.

"We now have a drug that can bring many people back from a downward curve with no hope for resurrection of the immune system and no hope for control of the virus," said study author Dr. Roy Steigbigel, head of the HIV Center at Stony Brook University.

The federal government has already approved raltegravir for use in so-called "salvage therapy," based on early findings from this study. But the completed research -- funded by Merck & Co., the drug's manufacturer -- shows that the raltegravir continues to work over time, Steigbigel said.

While AIDS has become much more treatable over the past 12 years, thanks to a new generation of drugs, some patients continue to develop resistance to medications. Despite the medical advances, the AIDS virus in the body can learn to evolve into new forms that aren't susceptible to the killing power of drugs.

Patients who don't follow their drug regimens to the letter are most likely to become immune to the drugs, but even the most careful patients can develop resistance, Steigbigel said.

To complicate matters, some patients are immune to drugs, because they were infected by someone with a resistant strain of the AIDS virus.

Raltegravir is unique, because it's part of a new class of AIDS drugs, meaning the virus hasn't encountered it before. "There aren't going to be viruses out there that are resistant to this," Steigbigel said. "That's why it's considered somewhat of a breakthrough."

In the new study, AIDS patients randomly received either raltegravir or a placebo. The patients all received doses of other drugs that are routinely prescribed to help patients in their conditions.

At the 16th week of the study, 62 percent of 458 patients who took raltegravir saw their HIV levels drop to a low level -- below 50 copies per milliliter. Only 35 percent of those who took the placebo saw their levels go that low.

The levels remained consistent when patients were tested at the 48th week. As for side effects, there were about as many among both groups.

Rowena Johnston, vice president of research for The Foundation for AIDS Research, said the development of better treatments for drug-resistant AIDS patients is crucial.

"Rates of drug resistance have increased steadily in the developed world because of the difficulties associated with adhering to treatment regimens," she said. "This problem will surely be multiplied several-fold as patients in the developing world are exposed to antiretroviral therapy for increasing lengths of time."

SOURCES: Roy Steigbigel, M.D., professor, medicine, and chief, HIV Center, Stony Brook University, N.Y.; Rowena Johnston, Ph.D., vice president, research, Foundation for AIDS Research, New York City; July 24, 2008, New England Journal of Medicine