Although the experimental drugs Virazole and AZT may be useful in treating the deadly acquired immune deficiency syndrome, AIDS researchers say that the two medications appear to be less effective when used together and that the combination of the two could even be harmful.
Virazole, known generically as ribavirin, is manufactured by Costa Mesa-based ICN Pharmaceuticals Inc. In January, ICN released partial results of clinical trials indicating that the drug may slow the onset of full-blown AIDS in people infected with the virus.
But, in a report published last week in the journal "Science," researchers at Boston's Massachusetts General Hospital said they tested AZT and Virazole in several different human cell cultures and found they "antagonized" one another.
"It is conceivable that this mechanism happens in people as well," Dr. Markus W. Vogt told the Associated Press. "This should be tested in animals before trying the combination in humans."
A spokesman for ICN declined Monday to comment about the experiments.
AZT, made by the Burroughs Wellcome Co., of Research Triangle Park, N.C., is currently one of the most promising anti-AIDS drugs to emerge. In January, a Food and Drug Administration advisory panel recommended that AZT receive prescription approval.
The Boston researchers cautioned that desperate patients with the fatal disease who obtain the experimental drugs illegally may harm themselves if they mix the two.
"I am afraid that both AZT and ribavirin are or will be available on the black market, particularly in large cities on the East and West Coasts," said Dr. Martin S. Hirsch, head of AIDS research at the hospital. "It is a natural temptation for people who are desperate and fear for their lives to attempt to combine these drugs."
The researchers, including scientists from Burroughs Wellcome, said they had hoped that by combining Virazole with AZT, the two drugs would be more powerful than either would be if administered individually.
"To our surprise, the combination proved antagonistic," they said in the article, published last Thursday.
Virazole, the researchers said, appears to prevent the necessary chemical changes in AZT that are required for the drug to interfere with reproduction of the virus which causes acquired immune deficiency syndrome.
In a multistaged process, AZT must pick up phosphorus to become active against viral reproduction, Vogt said. Virazole, which goes through the same process, seems to compete with AZT to decrease its effectiveness, he said.
Moreover, Virazole and AZT, when used together, could potentially "accelerate" the sometimes-harmful side effects associated with one another, James Fyfe, one of the Burroughs Wellcome researchers participating in the study, said Monday.