July 8, 1999 ANN ARBOR -- An antiviral drug administered once daily during flu outbreaks may be useful in preventing type A and B influenza, according to a new study by a University of Michigan School of Public Health professor. The study appears in the July 7 issue of the Journal of the American Medical Association (JAMA).
Dr. Arnold S. Monto and colleagues studied the use of the drug zanamivir as a preventative for the flu. A total of 1,107 healthy adults from Ann Arbor and Columbia, Mo., participated in a study in which half received a placebo and half inhaled 10 milligrams of the drug zanamivir once a day for four weeks during local flu outbreaks.
"Zanamivir is the first of a class of antiviral drugs that inhibit both type A and B influenza. Vaccines are effective and should be used, but there are situations in which we need to have antiviral drugs for prevention. Taken once a day, zanamivir is very effective in preventing of influenza and is definitely safe. These drugs are especially useful when we have outbreaks caused by both type A and B viruses," Monto said.
The drug was found to be 67 percent effective in preventing laboratory-confirmed clinical influenza infection. It was found to be 84 percent effective in preventing laboratory-confirmed illnesses with fever. Of the people studied, 14 percent had received a flu vaccination prior to participating in the trial.
Zanamivir has been demonstrated to be effective in clinical trials in shortening the duration and reducing the severity of type A and B flu.
The authors write that use of drugs as a preventative for flu as an adjunct to vaccination has been considered useful in specific situations and will continue to be the case. "One of these situations was exhibited in 1997-98, when a change in the circulating virus limited the efficacy of the vaccine. Another would be when a person in the risk groups recommended for vaccination is found to be unvaccinated by medical personnel after influenza transmission has started. In this case, vaccine could be administered and the drug given and continued for at least the limited period while antibody develops."
To date, there have been two antiviral drugs--amantadine and rimantadine---found to be effective in preventing the flu. However, the researchers say there have been concerns about those drugs. "Concerns raised included the lack of effectiveness against type B viruses, occurrence of adverse effects mainly related to amantadine, and the rapid development of resistance to both agents," the authors write.
This study was supported financially by Glaxo Wellcome Inc., Research Triangle Park, N.C.
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