The World Health Organization has taken three generic AIDS drugs off its list of approved products. It's the second time in three months the WHO has taken such a step.

The drugs taken off the WHO's list are antiretroviral pills made by India's Ranbaxy Laboratories. Two generic AIDS drugs from another Indian company, Cipla, were removed from the list in May. In both cases, WHO inspectors found problems with the reliability of tests measuring how much of the drug is absorbed into a patient's bloodstream.

Generic drugs advocate Rachel Cohen of the humanitarian group Doctors Without Borders says it's important to note that the WHO found problems with the companies testing the drugs for Ranbaxy and Cipla, not with the drug makers themselves. "There's a paperwork problem here. There's not actually necessarily proof that there's anything wrong with the medicines," she says.

Still, the move has forced Doctors Without Borders and other groups using the de-listed drugs to switch to alternatives.

The Bush Administration has focused attention on the WHO's approval system, and on low-price generic AIDS drugs in general, by refusing to purchase them for its multi-billion dollar global AIDS relief program. Critics say the policy favors U.S.-based brand-name drug makers. But chief medical officer Joseph O'Neill in the U.S. Global AIDS Coordinator's office says the de-listings back up the administration's position. "It's a pretty good demonstration of why we felt it was so important that there be regulatory review of medications before we purchase them," he says.

Dr. O'Neill says U.S. AIDS relief programs will only purchase medications approved by the U.S. Food and Drug Administration, or FDA.

But the head of the WHO's drug inspection program, Andre van Zyl, bristles at the suggestion that his agency's system is inferior to the FDA's. He says the WHO found the problems at the testing companies by using the same inspection procedures as the FDA uses. He says the de-listings show the strength of the WHO scheme. "The fact that we have exposed problems I think just shows that we have a rigorous process in place, and that our ongoing monitoring process is working. Of course, there may be lessons learned from this, and we take note of that, and we may improve on the process we are following," he says.

Rachel Cohen from Doctors Without Borders says the incident has made her more confident in the WHO system, not less. And she adds the United States ought to be helping to build up the WHO scheme. "Rather than just looking at this as just empirical evidence of something that needs to be improved, that needs to be worked on, it's being manipulated for political purposes to say 'I told you so.' That's not fair for people with AIDS whose lives depend on a sustainable supply of quality, affordable medicines," she says.

The WHO de-listings have not left the AIDS medicine cabinet bare. Among the remaining options is another generic combination pill, also made by Cipla. WHO inspectors recently found no problems with the tests on that product. Doctors Without Borders recently published a study on that pill in the journal The Lancet which showed it was effective in a small group of patients with AIDS.

Both Cipla and Ranbaxy say they plan to have the de-listed products re-tested, and expect them to be back on the WHO list soon. Ranbaxy is also seeking approval for its products from the FDA.