"In that context, Tamiflu is a risk factor for the emergence of resistance," he explained.
Boivin said that one-third of the known cases of H1N1 virus resistant to Tamiflu have been among people already exposed to the pandemic flu. "Another third emerged in imuno-compromised [weakened immune system] patients who received prolonged therapy with Tamiflu," he said.
The mutation of the H1N1 virus that caused its resistance to Tamiflu was the same one that was found in seasonal flu resistant to the drug. Last year, one strain of the seasonal flu was resistant to Tamiflu, Boivin said.
"You should be careful when you use post-exposure prophylaxis," Boivin said. In most cases, Tamiflu should be reserved for early treatment of flu when symptoms develop, he said.
Dr. Marc Siegel, an internist and associate professor of medicine at New York University Langone Medical Center in New York City, said that "Tamiflu prophylaxis given to the wrong people can increase your risk of a resistant strain developing -- and that's the last thing we need."
Siegel thinks, however, that Tamiflu used correctly can help prevent people from getting the flu, especially when the vaccine is in short supply.
"In the absence of available vaccine, one of the ways you can cut down on the spread of H1N1, to people you feel are at risk, is with the proper use of Tamiflu prophylaxis," he said.
Another expert, Dr. Pascal James Imperato, dean and Distinguished Service Professor of the School of Public Health at SUNY Downstate Medical Center in Brooklyn, N.Y., said that "based on our current knowledge, it appears that resistance of influenza viruses to the anti-influenza drug Tamiflu occurs in a setting of drug overuse
All rights reserved