The U.S. Food and Drug Administration (FDA) is best known for protecting public health by ensuring the safety of the national food supply and the safety and effectiveness of human drugs, biologics and medical devices. In addition, however, the agency helps safeguard the health of food-producing animals, thereby contributing to the safety of such important staples as meat, milk and eggs.

The FDA's Center for Veterinary Medicine (CVM) reviews drugs used in all farm-raised animals, including cattle, hogs, chickens and fish, as well as family pets. During 1999, CVM reviewed nearly 6,000 applications for approval of new or generic drugs, or for a change in the indications of an existing drug. An overview of FDA activities that improve the safety of human food derived from animals follows.

Residues

The CVM approves drugs for food-producing animals that may be dispensed over the counter or with a veterinarian's prescription. These drugs may be given in a dosage form or in feed or water. In all cases, approval is based on scientific determination that no unsafe residues or metabolites will result when the drug is used in the approved manner, and large safety margins are factored into the approved levels of use.

When animals are slaughtered, the U.S. Department of Agriculture (USDA) has the responsibility for testing the meat and, in the rare instances of a residue in violation of standards, the FDA investigates. Livestock producers who are first-time offenders are typically visited by federal or state investigators who look for the reason for the residue and teach the producer how to avoid similar problems in the future. Repeat violators may be tried and sentenced to prison terms.

Antimicrobial Resistance

Another concern linked to the use of antimicrobials in food-producing animals is the potential for development of resistance in human pathogens that are transmitted to humans via animal-derived food. Evidence of potential public harm from antimicrobial resistance is growing. The CVM has determined that it must develop a new approach to protecting public health while providing for the safe use of antimicrobials in food-producing animals.

The regulatory tools used by the CVM in the past were designed to assess the toxicologic safety of chemical compounds. With antimicrobial agents, however, safety is more difficult to determine because, in addition to toxicologic safety, the CVM must assess the safety of the use of antimicrobials in food-producing animals.

In November 1998, the CVM announced that it would begin to evaluate antimicrobial products based on the quantity of resistant bacteria that could be created by each product's use and on the changes in the number of animal enteric bacteria that are human pathogens. The “Framework Document,”¹ issued the following month, described the CVM's considerations involving its regulatory approach to antimicrobial resistance and discussed the concept of antimicrobial risk management.

The concept, which is now being implemented, calls for the establishment of monitoring and resistance thresholds before a drug can be approved. Once resistance to a drug crosses a predetermined monitoring threshold, the CVM will ask the drug sponsor to provide additional information to determine which uses, husbandry practices and other factors are most responsible for promoting the development of resistance. Precautions to mitigate future increases in resistance would then be put in place. If resistance continued to increase to a predetermined resistance threshold level, the CVM could take regulatory actions, up to and including restrictions on the drug's use or removal of the drug from the market.

Bovine Spongiform Encephalopathy

The CVM is also responsible for protection against animal feed that can affect the safety of derived human food. In recent years, the spread of bovine spongiform encephalopathy (BSE), the so-called “mad cow disease,” in the United Kingdom has prompted the CVM to place restrictions on the production of several types of feed. The action was based on research indicating that BSE is transferred among cows through feed made from the rendered carcasses of cattle that contain a prion that has been linked to BSE. The seriousness of the problem was magnified by the emergence in the United Kingdom of the human illness “new-variant Creutzfeldt-Jakob disease,” which gave rise to a scientific theory that BSE can be transferred to humans.

Although BSE has not been identified in the United States, the CVM has banned the use of mammalian tissues such as meat, bone meal, meat byproducts and cooked bone marrow in feed for cattle and other ruminant animals. The implementation of the ban is verified through intensive inspection of rendering plants and feed manufacturers.

Irradiation

The FDA has approved irradiation of meat and poultry and allows the process to be used for a variety of other foods, including fresh fruits, fresh vegetables and spices. During irradiation, foods are exposed briefly to a radiant energy source such as gamma rays or electron beams, a procedure that has been determined by the agency to be safe and effective in decreasing or eliminating harmful bacteria. Irradiation also inhibits sprouting, reduces spoilage bacteria, insects and parasites, and delays ripening in certain fruits and vegetables.

The FDA has also approved irradiation of bagged laboratory animal feeds for general microbial disinfection and to prevent microbial contamination. Poultry feed and feed ingredients are treated to render these products negative for Salmonella. In addition, the CVM is considering the merits of a recent petition calling for the use of irradiation for general microbial disinfection of feeds and feed ingredients.