Common Flu Strain Resistant to Popular Antiviral Drug

Bresee noted there are alternatives to Tamiflu, including Relenza (zanamivir) made by GlaxoSmithKline. "The viruses that we are seeing that are resistant to Tamiflu are sensitive to zanamivir," he said.

Zanamivir has some limitations, Bresee said. It can't be given to young children and patients with certain lung diseases.

Other treatment options include the antiviral rimantadine (brand name Flumadine).

Bresee added that all the circulating flu stains are prevented by the flu vaccine, and it's not too late to get vaccinated. "Folks who haven't gotten the vaccine so far can still go get it," he said.

Dr. Pascal James Imperato, dean and Distinguished Service Professor of the Graduate Program in Public Health at SUNY Downstate Medical Center in New York City, thinks resistance to Tamiflu developed because of its use in other countries to treat upper respiratory infections.

"The emerging resistance of H1N1 influenza strains to oseltamivir was first noted a few years ago," Imperato said. "At present, based on analyses of H1N1 isolates from 16 countries in 2008, some 31 percent demonstrated resistance to Tamiflu."

Tamiflu resistance has not been documented for the two other common current human influenza strains, H3N2 and influenza B, or for avian influenza (H5N1), Imperato said.

"On the face of it, the emergence of resistance in the presence of limited drug use would seem unusual," Imperato said. "However, in many areas of the world, there is significant Tamiflu use for upper respiratory infections. It is believed that minor mutations in the H1N1 virus can in effect block the action of Tamiflu," he said.

It is important to note that no H1N1 influenza resistance to Relenza has developed, Imperato said. "This is the other drug in the neuraminidase group used to prevent and treat influenza," he said.

Flu usually causes about 36,000 deaths in the United States each year. Most deaths are among the elderly, very young or those with medical conditions such as asthma or heart disease. Pneumonia resulting from flu is usually the fatal complication.

More information

For more on the flu, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Joseph Bresee, M.D., chief, Epidemiology and Prevention Branch Influenza Division, U.S. Centers for Disease Control and Prevention, Atlanta; Pascal James Imperato, M.D., M.P.H., Dean and Distinguished Service Professor, Graduate Program in Public Health, SUNY Downstate Medical Center, New York City