The Food and Drug Administration wants to prohibit the extra-label use in poultry of two classes of approved human antiviral drugs in treating influenza. The reason? The agency says the measure is necessary to help preserve the effectiveness of these drugs for treating or preventing influenza infections in humans.

Specifically, the order prohibits the extra-label use by veterinarians of anti-influenza adamantane and neuraminidase inhibitor drugs in chickens, turkeys, and ducks. Extra-label use is the use of a drug in a manner that is not in accordance with the approved labeling.

"Todays action is a preventive measure designed to protect the public health and illustrates FDAs high level of commitment and key role in preparing for a possible influenza pandemic, which is a top priority for our nation," said Acting FDA Commissioner Dr. Andrew von Eschenbach.

Currently, no drugs are approved for the treatment or prevention of influenza A in animals. However, two classes of antiviral drugs are approved in the United States for the treatment or prevention of influenza A in humans. Under the Animal Medicinal Drug Use Clarification Act of 1994 (AMDUCA) veterinarians can legally prescribe these human antiviral drugs to protect animals from influenza.

Under AMDUCA and its implementing regulations, FDA can issue an order prohibiting certain extra-label uses in animals if such extra-label use presents a risk to the public health. FDA has considered all available information and has concluded that the extra-label use of anti-influenza adamantane and neuraminidase inhibitor drugs in chickens, turkeys, and ducks presents a risk to public health.

FDA may add other animal species to the prohibited list as new data becomes available.

Thus far, there have been no reported cases of avian influenza H5N1 in the U.S. Nor is FDA aware that there is ongoing extra-label use of these antiviral drugs in the U.S. by poultry producers. However, concerns have been raised by a number of public health organizations, such as the World Health Organization, Food and Agriculture Organization, and the World Animal Health Organization, that the extra-label use of these drugs in poultry could lead to the emergence of resistant strains of type A influenza.

This is of particular concern if the avian influenza H5N1 (commonly known as bird flu) that has been identified in other countries were to emerge in the U.S.

Influenza viruses mutate frequently. Some mutations confer drug resistance to influenza viruses. Repeated and improper use of anti-influenza drugs could allow resistant influenza viruses to flourish.