Two drugs that separately may be somewhat useful against AIDS show noticeably less effectiveness--and may even harm patients--when used together, scientists say.
Researchers at Boston's Massachusetts General Hospital and elsewhere reached this conclusion after testing the two drugs, AZT and ribavirin, in several different human cell cultures and found that the two agents antagonized one another.
"It's conceivable that this mechanism happens in people as well," Dr. Markus W. Vogt warned. "This should be tested in animals before trying the combination in humans."
The researchers cautioned that desperate AIDS patients 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," said Dr. Martin S. Hirsch, head of AIDS research at the Boston hospital. "It is a natural temptation for people who are desperate and fear for their lives to attempt to combine these drugs."
The researchers said it appears that ribavirin prevents necessary chemical changes in AZT that are required for the drug to interfere with reproduction of the virus that causes acquired immune deficiency syndrome.
AZT, which reduced the symptoms and death rate of patients with AIDS in trials last year, is being taken experimentally by thousands of patients.
Ribavirin is thought to have some effect in preventing or delaying the onset of AIDS in people who have been infected with the virus but who may not be sick.
In a recent report in Science magazine, the researchers said the drug-mixing results were unexpected. They said they had hoped the combination would produce a synergistic effect. "To our surprise, the combination proved antagonistic," they wrote.