TORONTO - U.S. scientists are reporting the first case of resistance of the H1N1 flu virus to the first new flu drug to hit the market in about a decade.

The scientists report that an H1N1 patient whose infection developed resistance to Tamiflu also developed resistance to the new drug, Peramivir.

The scientists, who work for the U.S. National Institute of Allergy and Infectious Diseases, are reporting on the treatment of two immunocompromised patients who quickly developed resistance to Tamiflu during treatment.

One also developed resistance to Peramivir and the scientists are warning doctors to be on the lookout for quick development of resistance when treating immunocompromised patients.

The U.S. Food and Drug Administration gave intravenous Peramivir an emergency use authorization last October in the middle of the second wave of the pandemic.

The World Health Organization says 267 cases of Tamiflu-resistant H1N1 have been seen since the pandemic emerged last spring.