Also known as dideoxycytidine and zalcitabine, DDC is the third AIDS antiviral drug to be licensed since 1987, when AZT was approved. Last fall, the FDA approved the antiviral DDI.
Antiviral drugs are considered the major tools in the fight against AIDS because they attack the underlying viral condition, rather than the individual infections and other illnesses that result from a damaged immune system. Most AIDS researchers believe that the key to controlling AIDS ultimately lies in developing an effective combination of antiviral therapies.
"This drug approval represents another step forward for patients with AIDS," Secretary of Health and Human Services Louis W. Sullivan said yesterday in a statement. "Zalcitabine has been rapidly developed, tested and reviewed through the cooperative efforts of scientists in the federal government, academia and the pharmaceutical industry."
The drug is manufactured by Hoffmann-La Roche Inc., of Nutley, N.J.
The agency based its decision on studies showing that the combination regimen produced a dramatic and sustained rise in the number of CD4 cells -- the critical immune system cells that are the primary target of the Human Immunodeficiency Virus -- compared with patients taking AZT alone.
Early evidence that a drug elevates CD4 cells is not necessarily an indication of how effective a drug will be. However, an increase in CD4 cells is believed to indicate that the body's disease-fighting ability has been at least transiently enhanced.
The agency used the same criteria when it approved DDI.
The FDA, which has been seeking to speed AIDS drugs to the market as rapidly as possible, has become increasingly willing to rely on these so-called "surrogate markers" to approve drugs.
In a sign of the agency's efforts to speed up approval of AIDS drugs, the action came only eight months after the company submitted its application for licensing. And it was only two months ago that an FDA advisory committee recommended that the agency approve the two drugs to be used in combination therapy -- an unusually rapid timetable. Most drug approvals take an average of two years.
"This is particularly heartening because it shows the FDA is continuing its innovative approaches to evaluating AIDS therapies," said Dr. Robert T. Schooley, an AIDS researcher at the University of Colorado who has conducted studies of DDC.
Dr. Margaret A. Fischl, who directs AIDS programs at the University of Miami school of medicine, called the combination treatment "a major advance in the treatment of HIV infection.
"The data from a small study have shown that combination therapy was well-tolerated and that the side effects were no different than we would have anticipated with either drug alone," she said.