WASHINGTON -- Setting the stage for possible federal approval of a third antiviral AIDS drug, early findings in an ongoing study have shown that the experimental AIDS drug DDC, used in combination with AZT, produces more than twice the crucial immune system cells as does AZT used alone.
The findings were presented yesterday to a Food and Drug Administration advisory panel that is expected to vote today on whether to recommend approval of DDC, which is manufactured by Hoffmann-La Roche Inc., of Nutley, N.J. Although recommendations by advisory committees are not binding, the FDA almost always follows their advice.
If approved, DDC would become the third licensed antiviral drug in the AIDS arsenal.
Antiviral drugs, which are considered the "big guns" in the fight against AIDS, attack the underlying virus, unlike the drugs that fight the opportunistic infections and other conditions that result from an impaired immune system. Most researchers believe that the key to controlling AIDS ultimately lies in developing a successful combination of antiviral therapies.
AZT, which is manufactured by Burroughs Wellcome Co., was approved in 1987; DDI, made by Bristol-Myers Squibb Co., was approved last fall.
The latest findings are important because the same kind of evidence -- an increase in CD4 cells, the primary target of the human immunodeficiency virus -- served as the basis for the agency's recent approval of DDI. Subsequent findings, released at a meeting of AIDS researchers last week, showed that DDI was more effective than AZT in slowing the progression of the disease in individuals who had been treated with AZT, although there was no difference in overall survival.
The latest study also appears to confirm the findings of a study published in January that showed similar increases in CD4 cells but that was met with reservations because it involved far fewer study participants.
"The FDA wanted the CD4 cells analyzed [in the latest study] to see if the rise correlated with the earlier study," said Dr. Robert T. Schooley, head of the infectious diseases division at the University of Colorado Health Sciences Center, who presented the data. "It does. Over the first six months, the rise on both drugs [DDC and AZT] was roughly twice as much as with AZT alone."
Early evidence that a drug elevates CD4 cells is not necessarily an indication of how effective a drug will be. But it apparently has been reliable to some extent for both AZT and DDI, both of which have proved beneficial to patients.
If DDC, or dideoxycytidine, is licensed, it is likely to be approved for use only in combination with AZT. Clinical studies of DDC used alone have shown it to be less effective than AZT. In fact, one study was halted last year because it showed that the risk of dying was far greater for patients on DDC than on AZT.