ROME, July 21 — A total recall of an important AIDS drug widely used in developing countries has disrupted treatment for tens of thousands of the world’s poorest patients, with no clear word from the manufacturer on when shipments will resume.

The recall of the drug, Viracept, by Roche Pharmaceuticals of Switzerland, went largely unnoticed in the developed world when it was announced in early June, after the company had discovered that some batches made at its Swiss plant contained a dangerous chemical. But the recall has caused growing concern among global health officials and in AIDS programs in many poor nations. They say the company did an inadequate job of informing patients and officials about the potential risks and helping them find affordable access to newer alternative drugs.

Roche said that it had been actively working with health officials across the globe and that the risk from the affected batches was low.

The scope of Roche’s recall is extraordinary, if not unprecedented, in the battle against the human immunodeficiency virus that causes AIDS, global health officials say. Dr. Lembit Rago, an official at the World Health Organization, said tens of thousands of people take Viracept worldwide, many of them poor people with H.I.V. in developing countries. The recall has left those patients with the painful choice of discontinuing a lifesaving medicine, or using a drug that might contain a dangerous contaminant.

Officials at the W.H.O. in Geneva and the European Medicines Agency in London said Roche had not provided information they consider essential for safeguarding public health: which countries the tainted medicine was shipped to, the concentration of the contaminant and what the company will do for its patients. The European agency, which regulates drugs for the European Union, has canceled Roche’s license to market the drug.

Dr. Rago called the recall “sort of a disaster” for patients in very poor countries. He said of Roche, “They failed in communication.” Roche has denied the accusation. The company, which had revenue of $35 billion last year, said it promptly notified health providers in the affected countries to discontinue use of the drug, which is dispensed in both pill and powder form. It also said it would cover the “reasonable costs” of the recall. It did not define “reasonable costs.”

So far, in some countries like Panama, patients or treatment programs have had to make up the difference in cost between Viracept and far more expensive alternatives. For some patients in other countries, like Venezuela, alternatives to Viracept are unavailable.

Roche said the recall affected “Europe and some other world regions” but has not been more specific. The recall does not affect the United States, Canada or Japan, where a version of Viracept is made by Pfizer. Roche has been in discussions with Pfizer about supplying Pfizer’s version to some affected countries, but regulatory and licensing issues could take “some time,” said Martina Rupp, a Roche spokeswoman.

Roche sells Viracept for use in low-income countries at the discounted median price of about 28 cents a dose, according to the W.H.O.’s 2006 global price reporting system for AIDS medicine. The drug, also known as nelfinavir, is a member of the class of AIDS drugs known as protease inhibitors. It is considered an important defense against H.I.V., but it has fallen out of favor in Europe in recent years compared with newer medicines that are more convenient and cause fewer side effects.

In some places, newer substitutes are not available to patients, either because they are not licensed or are much more expensive, said people with H.I.V. and international health experts. In Panama, for example, a substitute drug, Kaletra, costs three times as much as Viracept.

“Roche has provided information, but there has been much less support in terms of who is going to pay the additional cost,” said Dr. César Nu?ez, the United Nations AIDS program’s coordinator for Latin America, who is based in Panama.

A more limited recall might have been possible had Roche been more forthcoming about the countries affected and the lots that were suspect, said Dr. Rago, the W.H.O. coordinator of quality assurance and safety for medicines. “It’s fine for Roche to say ‘withdraw and replace,’ but there may not be much else at hand to substitute” in many places, he said. “This is not just about Europe.”

In response to questions sent by e-mail, Ms. Rupp said Roche had shipped “at least one packet of Viracept with high levels of the impurity to 35 countries.” But she declined to say which countries because Roche regards such information as proprietary. High levels of the contaminant “were observed in batches of Viracept that had been released to countries since March 2007,” she said.

The company made the recall worldwide “in order to avoid confusion,” she said. Roche estimates that about 45,000 patients were affected by the recall. Ms. Rupp said the toxic substance, ethyl mesylate, should be called an “impurity” rather than a contaminant because it was created in the manufacturing process and because that type of chemical can be found in very low levels in other medicines, although it was not supposed to be present in Viracept.

The company was performing studies on the issue, but the results would not be available for “some months,” she said. At high doses, ethyl mesylate has been shown to cause cancer in animals, and at lower levels it can cause genetic mutations, which means children and fetuses are particularly vulnerable.

Asia Russell, the coordinator of international advocacy for Health Gap, a nongovernmental organization based in New York and Philadelphia that focuses on medical care in the developing world, said, “It seems that Roche has abandoned these patients, since in many places there aren’t ready alternatives.”

In Venezuela, 3,000 people were on Viracept, paid for by the national health service, and the effect of the recall was “severe,” because many had no other options, said Edgar Carrasco, an advocate on issues relating to AIDS in Caracas.

Alberto Nieve, another advocate, said Roche had promised to make a donation of another medicine. “Most people are still waiting,” he said. “They have not switched yet, especially outside Caracas.”

In the month since the recall, officials at the European Medicines Agency and the W.H.O. said that they, too, would like more information from Roche about the dose of the contaminant and where exactly the medicine was sent.

“We have not gotten information, not even an order of magnitude,” said Martin Harvey-Allchurch, a spokesman for the European agency. “I understand sales figures are confidential, but I would have thought by now we would have this information.”

Viracept was sold in 49 countries since 2004, according to the W.H.O., with more than 12 million units sold in 2006 and 2 million in 2007. Tido Von Schoen-Angerer, director of the essential medicines campaign at Doctors Without Borders, said about half of the 400 patients who received therapy supplied by the group in Africa were on Viracept. The alternate from Abbott is not yet available, he said.