The World Health Organization, saying it can't assure the quality of several tuberculosis products made at a Wyeth (WYE) plant in Pakistan, will suspend purchases of the drugs.

Wyeth Pakistan Ltd., a unit of Wyeth, introduced new active ingredients into the medications and changed the storage conditions without getting approval of the WHO, according to a letter the agency sent the company on Monday. The letter was posted online Tuesday.

The suspension affects four drugs manufactured at the plant that are used to treat tuberculosis, a deadly infectious disease that commonly affects the lungs.

Although it's unclear exactly how the suspension will affect Wyeth, it likely means a host of aid agencies across the globe will stop purchasing the medicines, said Roger Bate, Legatum fellow at the American Enterprise Institute.

Wyeth spokesman Doug Petkus said the facility has about 300 employees and serves as an administrative and manufacturing plant. He said the company has just received the notification and is reviewing it. Wyeth will work with WHO to address the matters, he said.

The tuberculosis drugs are made and distributed under a WHO program started in 2001 that gives third-world countries access to safe, effective and quality medicines.

The WHO letter says that it inspected Wyeth Pakistan's facility in 2005 and found that it wasn't complying with good manufacturing practices to ensure the quality of medicines. It's unclear whether the company has since brought its manufacturing practices in line with those standards. A WHO spokesman wasn't immediately available to comment.

These type of letters from the WHO, called notices of concern, aren't cause for public concern. If WHO identifies a public health risk, it will take other steps to alert the public.

Bate said, however, "this is not good for Wyeth." He said aid agencies, such as the United States Agency for International Development, often make decisions months ahead of time about where it will buy products to distribute to underprivileged countries.

"The impact on the company is often bad because at any one moment people across the world will be considering [where] to procure drugs, and Wyeth is off the table," Bate said.

-By Jared A. Favole, Dow Jones Newswires; 202.862.9207; jared.favole@dowjones.com