Many people infected with HIV are living longer thanks to a drug treatment regimen that keeps the virus from developing into AIDS. International pressure forced drug companies to bring down the cost of the drugs to make them widely accessible. But now a new line of drugs has been developed and aid groups are asking drug companies to lower their costs as well.

When the first anit-AIDS drugs were introduced more than a decade ago in the western world, the cost was prohibitive at around $10,000 per year.

But competition, international pressure and the manufacture of generic drugs drove down the cost of treatment to around $130 a year, making it possible to treat millions of HIV-positive people in resource-poor countries.

Now, the first-line drugs have started to fail in some cases, or cause serious side effects. A new line of drugs has been developed that is less toxic, but has the same effect of suppressing hiv to prevent it from developing into aids.

The World Health Organization has called for all patients who need them to have access to the new drugs.

The group estimates that between one and four percent of the patients its doctors treat need the more expensive second-line drugs.

But Nathan Ford of Doctors Without Borders' Thailand campaign says they are not available.

"If we want to provide long-term quality care for our patients, if they suffer toxic events and need to switch to a newer drug, or if they develop resistance and need to switch to a second-line medicine, then we're back to the pre-2000 era, where drugs are very, very expensive, and we have to fight with companies to get a more affordable source of these drugs," he said.

Ford says he's tired of asking drug companies to lower their prices.

"We're health care workers and peer educators working on the front line and it's not our job to be hassling drug companies in the U.S. just because we want to treat the patients," he said.

The U.S.-drug company Abbott Laboratories announced at the conference that it is reducing the price of its anti-viral drug, Kaletra, in 45 low-to low-middle income countries, including Thailand, to $2,200 per patient per year.

The company already makes the drug available in Africa and the poorest countries for $500 per patient per year.

Ford and others at the conference, said the price should come down even more.