BETHESDA -- Although they couldn't explain why, scientists said yesterday that a new drug capable of preventing many AIDS patients from losing their sight also helps the patients live longer.
The surprising result grew out of a nationwide clinical trial that included patients at the Johns Hopkins Wilmer Eye Institute. Doctors wanted to compare the effectiveness of an experimental drug, foscarnet, against an older drug, ganciclovir, in arresting a blinding condition known as CMV retinitis.
Doctors found that the two drugs were equally effective in halting the progress of the eye disease but that patients taking foscarnet lived an average of four months longer than those taking ganciclovir.
"In addition to making the quality of life better with either drug, we found that foscarnet prolongs lives," said Dr. Douglas Jabs, the study chairman, who is an associate professor of ophthalmology at the Johns Hopkins School of Medicine.
The findings of the study, which involved 240 patients at 12 medical centers across the country, were announced yesterday at the National Eye Institute in Bethesda, which sponsored the research.
Despite its life-extending potential, foscarnet is not considered an appropriate treatment for acquired immune deficiency syndrome patients who do not have the eye disease because it must be administered daily through an intravenous line into the chest. Among otherrisks, the tube presents a possible avenue for infection.
Foscarnet, produced by Astra Pharmaceutical Products Inc. of Westborough, Mass., was approved by the Food and Drug Administration Sept. 27.
After taking foscarnet, patients lived an average of 12 months. In contrast, patients assigned to ganciclovir lived eight months after they started taking the drug.
The eye disease is caused by the cytomegalovirus, which invades the retina and causes an ever-wideninghole in the victim's vision. The virus, which rarely afflicts people who do not have AIDS, strikes about 20 percent of all patients with acquired immune deficiency syndrome.
Dr. Jabs said the results mean that foscarnet is a better initial treatment for most patients, although it should not be taken by people with kidney problems because the drug can damage the kidneys.
Ganciclovir, in turn, cannot be taken with AZT, a drug that has been shown to slow the spread of the AIDS virus.
That problem has forced many patients to choose between the possibility of living longer with AZT or preserving their sight with ganciclovir.
It could be that the patients on foscarnet lived longer because they were able to continue taking AZT, Dr. Jabs said.
But that doesn't fully explain the extended lives of the foscarnet patients, he said. Doctors pointed out that many patients on foscarnet were not taking AZT yet lived longer.