Effectiveness of AIDS Drugs Compared : Health: Early analysis of study indicates that DDI may be better than AZT in slowing symptoms of the disease. Research raises questions about treatment.

DDI appears to be more effective than AZT in slowing the progression of AIDS symptoms, according to the preliminary analysis of a study comparing both antiviral drugs in individuals previously treated with AZT.

The results, which were presented Monday to AIDS researchers at a meeting here, will now be further analyzed before specific recommendations regarding treatment with DDI will be made.

The latest findings are expected to raise numerous questions for patients already on AZT, among them, whether they should now switch to DDI.

“The data from this study are believable and very powerful,” said Dr. James Kahn, assistant clinical professor of medicine at UC San Francisco, the lead researcher. “This information needs to go out as quickly as possible.”

However, the practical application of the study, sponsored by the National Institute of Allergy and Infectious Diseases, is “something we’re still struggling with,” he said, adding that individual patients should discuss the research with their physicians to determine how the results could affect them.

Also, because the study only involved patients earlier treated with AZT, it is still unknown whether DDI is more effective than AZT in patients who have never taken AZT. A separate study comparing AZT and DDI in such patients is currently under way.

An antiviral drug is one that attacks the underlying viral condition--in this case, the human immunodeficiency virus--rather than the opportunistic infections, cancers and other conditions that result from the damaging effects of HIV on the human immune system.

DDI, also known as didanosine, or dideoxyinosine, and AZT, or zidovudine, are the only AIDS antiviral drugs licensed thus far by the federal government. DDI is manufactured by Bristol-Myers Squibb Co., and AZT is made by Burroughs Wellcome Co.

There were 913 patients enrolled in the study. Of these, 30% had fully developed AIDS, 60% were suffering from AIDS-Related Complex and 10% were HIV-infected but had not yet developed symptoms of the disease.

Those with AIDS and ARC had fewer than 300 CD4 cells per cubic milliliter of blood, while the asymptomatic group had fewer than 200. CD4 cells, also known as T helper cells, are the immune-system cells that are the primary target of HIV. A normal CD4 count ranges between 800 and 1,000.

Patients were divided into three groups--298 who took 500 milligrams of DDI only, 311 who took 750 milligrams of DDI only and a third group of 304 patients who took AZT only.

Overall, the group taking 500 milligrams of DDI showed the slowest progression of disease--a 33% difference in the rate of developing new AIDS conditions compared to the other groups, Kahn said.

The benefits were seen in the ARC patients and in the HIV-infected asymptomatic group, but not in patients with AIDS, Kahn said.

All the study participants previously had taken AZT for a minimum of 16 weeks, including many who had been on the drug for several years. The length of time on AZT did not appear to influence the outcome, meaning that it did not matter how long a patient had taken AZT before entering the study, researchers said.

Also, there was no difference in overall survival, researchers said.

The study also showed that patients on either dose of DDI experienced an increase of CD4 cells, compared to those receiving AZT.

The licensing of DDI by the Food and Drug Administration last year was considered a milestone in the drug-approval process because the decision was based on very preliminary research. The FDA, which has been seeking to speed new AIDS drugs onto the market, approved DDI largely on evidence that the drug raised the number of CD4 cells--not necessarily a reliable indicator that the drug ultimately would prove effective.

“This underscores the value of taking a chance on early data,” FDA Commissioner Dr. David A. Kessler said Monday. “The riskiest thing we can do when confronted with a disease like AIDS is be unwilling to take a risk.”

The study results are scheduled to be presented next Monday to the same FDA advisory committee that last year recommended that the agency approve DDI.