Drug ineffective against flu strain, scientists say

CHICAGO — As flu season hits high gear, doctors and public health professionals say treating cases is more complicated than ever because this year's most common strain has developed resistance to the drug known as Tamiflu.

The drug is one of only four antiviral medicines available to battle influenza, an illness that typically lands 200,000 Americans in the hospital, and kills 36,000 every year, according to the federal Centers for Disease Control. Scientists from the agency co-authored a paper on the resistance, which was published Monday in the Journal of the American Medical Association.

Because Tamiflu is no longer effective against the season's main flu strain, known as H1N1, physicians are turning to the other three antivirals, all of which have downsides.

Zanamivir, an inhaled drug known as Relenza, is not recommended for some of the very populations that would need it most: very young children and people with respiratory problems. Rimantadine, sold as Flumadine, and amantadine, sold as Symmetrel, have resistance troubles of their own.

With so many problems associated with antivirals, public health officials are urging people to get a flu shot, which they say offers good protection this year against the H1N1 strain.

"Flu season is still peaking," said Michael Koller, a doctor of internal medicine at Loyola University Medical Center. "There is no sign we are on our way down. It is not too late."

For most people who get the flu, antiviral drugs like Tamiflu aren't much help. Influenza is like a fast-moving wildfire that often burns itself out before the victim can obtain a prescription drug. But antiviral medications can be lifesavers for people most likely to develop serious complications from the flu — say, a grandparent in a nursing home.

Health professionals say Tamiflu-resistant flu is especially alarming for how fast it has spread. The virus managed to mutate into a resistant form and move around the globe within a year.

"It makes me nervous," Koller said. "We know that it keeps mutating and that is why it is still around. It manages to figure out ways to outsmart us and our medications."

Scientists began picking up hints about the strain's resistance during the last flu season, when reports of Tamiflu-resistant influenza came in from nations including Canada, Russia and Hong Kong. In the U.S., scientists found about 12 percent of the H1N1 viruses were resistant.