The U.S. Food and Drug Administration said Tuesday it is requiring the manufacturers of certain drugs used to prevent the rejection of transplanted kidneys to warn of certain serious infections.

The drugs, which include Roche Holding AG's (RHHBY) CellCept, Myfortic by Novartis AG (NVS) and Wyeth's (WYE) Rapamune, already carried the agency's toughest boxed warning discussing their various risks.

The FDA said the new drug labels must discuss an increased risk of "opportunistic infections," including activation of latent viral infections such as one caused by the BK virus.

The FDA said BK-virus infections, characterized by nephropathy, or a disorder of the central nervous system, can be serious enough to cause the kidney to be rejected.

The agency said a review of its adverse-event reporting system and the use of immunosuppressant drugs showed BK-virus infections were mostly seen in kidney-transplant patients.

The FDA said it was continuing to review the safety of immunosuppressant drug products.

Last year, Novartis and Roche updated the labels of Myfortic and CellCept to discuss postmarketing reports of a serious, often deadly neurological disease known as progressive multifocal leukoencephalopathy, or PML. The disease is caused by the activation of a common virus in the central nervous system, most often in immune-compromised individuals. The virus, known as the JC virus, sits latent in most adults.

-By Jennifer Corbett Dooren, Dow Jones Newswires; 202-862-9294; jennifer.corbett@dowjones.com