WASHINGTON - New flu strains show signs of resistance to pills doctors hope can slow a virus epidemic, suggests a study published Tuesday.
Researchers in Japan studied the effectiveness of the drugs, oseltamivir and zanamivir, during an influenza type B outbreak in the winter of 2005-2005.
They published the results of their study on the medications known by their trade names Tamiflu and Relenza in the US Journal of the American Medical Association.
Influenza type B is "associated with annual outbreaks of illness and increased death rates worldwide," and Tamiflu and Relenza are used more extensively in Japan to treat those outbreaks than anywhere else in the world, the study's authors said.
Researchers "identified a variant with reduced drug sensitivity in one (1.4 percent) of the 74 children who had received oseltamivir (Tamiflu)," the study said.
In 422 untreated patients, the influenza B virus was isolated and "found to have reduced sensitivity to zanamivir (Relenza), oseltamivir, or both" in seven, or 1.7 percent, of cases.
Tamiflu is produced by the Swiss lab Roche and Relenza by the British pharmaceutical giant GlaxoSmithKline. Both are used for flu prevention and treatment purposes.
Some cases of resistance to Tamiflu in influenza type A cases, which typically strike at the beginning of the flu season, have already been found but little information has surfaced about type B influenza and its reactions.
"The emergence of drug-resistant influenza B should draw attention to the importance of continual monitoring of strains over time and to the need for frequent rethinking of policies for use of antiviral drugs," an accompanying editorial said.
"Influenza viruses evolve rapidly and nimbly, which compels ongoing investigation of antiviral therapies that use alternative mechanisms of action and target different points in the viral life cycle."
04/03/2007 20:00 GMT