Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.

Reuters NewMedia, Inc.; Sunday May 31, 5:00 pm EST

"There is a problem with drug resistance, and we can't fool ourselves," said Stanford University's Dr. Robert Shafer, lead author of the new research published in the June 1 issue of Annals of Internal Medicine.

Shafer's team found that patients previously treated with multiple drugs to tackle HIV, the virus which causes AIDS, can develop full resistance to all available medications -- a finding which could indicate a developing "split" in the AIDS epidemic.

"There are the newly infected patients, who have benefited tremendously from powerful new drug combinations that can effectively shut down viral replication," the researchers said in a news release.

"And then there are the patients with HIV strains resistant to one or more drugs. The potent new drug combinations may not work in these individuals, for whom new approaches are needed."

The researchers conducted genetic analyses of viral samples taken from four patients infected with HIV-1, the most common U.S. strain of HIV. All of the patients had been on HIV drug treatment for between four and nine years.

They also tested 11 different drugs against the viral samples to determine whether the samples were susceptible to treatment.

All of the patients had initially taken the drug AZT and then added or substituted new drugs as they appeared, including the new class of protease inhibitor drugs which have shown promising results in preventing viral replication.

Shafer said the study revealed high resistance to five drugs, including three protease inhibitors, and a lower level of resistance to three other drugs, known as reverse transcriptase inhibitors.

"Over the six months, (the viral samples) were stable, they replicated well, and the (patients') viral loads remained high," Shafer said.

He said that although his study focused on only four patients, he had subsequently genetically sequenced viral samples from 400 patients in the San Francisco area and found largely similar results.

"We have to realize that there is so much cross-resistance that while there may be 11 approved drugs and three to four in the (drug development) pipeline, there really aren't 14 or 15 different options," Schafer said.

"The academic community has to face that and convince the drug companies of that. Unless we recognize the fact that certain things aren't going to work, there won't be the incentive to go back and develop new drugs."

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