Several new drugs work well in HIV patients who are beginning to run out of options because their virus has mutated into drug-resistant forms, researchers reported on Friday.

Adding new therapies to the 20 medications that already exist to control the AIDS virus is essential to keeping patients alive and healthy, because the virus almost always does mutate eventually, AIDS experts say.

And now that patients are starting to transmit drug-resistant infections directly to one another, it is more important than ever to have new drugs to suppress the virus, researchers told the 12th Annual Retrovirus Conference in Boston.

“I think in today’s arena any new agent is being considered as an addition to the armory,” said Dr. Mario Stevenson of the University of Massachusetts.

Combinations of HIV drugs called highly active antiretroviral therapy or HAART work very well to suppress HIV and keep it from damaging the immune system so badly that patients develop AIDS. But resistance develops eventually in many if not most patients.

Then new drugs are needed, and they must be different enough from the old drugs to avoid what is called cross-resistance.

One drug, still called by its experimental name TMC-114 by Tibotec, a subsidiary of drugs and personal products giant Johnson & Johnson, suppresses the virus well in patients who have been taking HAART for a while and who have developed resistance, the conference heard.

Dr. Richard Haubrich of the University of California, San Diego and colleagues tried a new cocktail in 497 patients, all but 100 or so of whom got varying doses of TMC-114, a new member of a drug class called protease inhibitors, with various other drugs.

The highest dose suppressed the virus back down to desirable levels, he told the meeting.

“This really shows remarkable results,” Haubrich said in a telephone interview.

A second Tibotec drug called TMC 278 is in a class called non-nucleoside reverse transcriptase inhibitors or NNRTIs.

An international team tested 47 men who had never taken any HIV drugs with varying doses of TMC 278 for a week.

It suppressed the virus and allowed immune system cells to recover, they reported. Now the team, lead by Frank Goebel of Ludwig Maximilians University in Munich, Germany, is testing the drug in patients who are failing in their current HAART regimens.

Dr. Susan Little of the University of California San Diego and colleagues tested Merck’s experimental drug in a new class of HIV drugs called integrase inhibitors. They help prevent the virus from infecting new cells.

Called L-000810810, the drug was tested in 30 HIV-infected patients. It worked effectively and safely both in patients who had taken HAART and stopped and those who had never taken any drugs, they told the meeting.