Prudent drug use in small ruminants (Proceedings)

With the constant introduction of new products on the human and veterinary market, it becomes a daunting task to keep up with veterinary pharmacology and vaccine technology. And although all veterinarians have the responsibility of safe and prudent drug use in animals, food animal veterinarians have the added responsibility of residue avoidance in food-producing animals. Most food animal practitioners are aware of the Animal Medicinal Drug Use Clarification Act (AMDUCA), but understanding what is actually allowed and what is not allowed can be difficult. This article will discuss the sometimes confusing rules and regulations of prudent drug use in food animals and provide resources that food animal veterinarians can use to find information.

What's Legal?

AMDUCA allows for extralabel drug use in food animals. But what is extralabel use? It is using a drug 1) in an animal species that is not on the label; 2) for a disease/indication that is not on the label; 3) at a dose level, frequency or duration that is not on the label; 4) by a route of administration that is not on the label; or 5) in a class of food animal that is not on the label. Therefore, using a drug in a goat that is only labeled for cattle (beef, lactating dairy, veal, etc.) is extralabel use. Using a drug in a dairy cow that is only labeled for beef cattle is extralabel use. Using a drug in a lactating dairy cow that is only labeled for nonlactating cows is extralabel use.

Constraints are associated with extralabel drug use under AMDUCA. Two of the most important are that extralabel use must be by or on the order of a veterinarian within the context of a veterinarian-client-patient relationship (VCPR), and that extralabel use must not result in violative residues in food-producing animals. For example, producers are not allowed to increase a dose of a drug, even if it is an over-the-counter product. Only a licensed veterinarian can do that. And veterinarians must have a valid VCPR even to prescribe drugs on label. For example, advising an unknown producer to give a dose of penicillin that is higher than the label indicates is not permitted, even though it is an over-the-counter drug. If a drug is prescribed in an extralabel manner, an extended withdrawal time must be established that prevents violative residues. Some resources to help establish proper meat and milk withdrawal times are the drug manufacturer for the particular product, clinical pharmacologists, testing protocols such as milk residue tests, and the Food Animal Residue Avoidance Databank (FARAD) at www.farad.org.

Other constraints to extralabel drug use in food animals are that the drug must not be on the prohibited list (see the next section); there must not be any drug(s) labeled for use in food animals that has the needed ingredient, in the proper dosage form, is labeled for the indication, and is potentially clinically effective.

A common question is, "When can a human-approved drug can be used in a food animal?" AMDUCA states that extralabel use of a human-approved drugs is not permitted if a drug approved for food animals exists that can be used in an extralabel manner. For instance, if a cephalosporin is indicated for a condition in a food animal, like neonatal septicemia in a calf, the veterinarian must use ceftiofur, since it is labeled for food animals, even though not for neonatal septicemia. If in this case culture results indicate no food animal drugs would be appropriate, another veterinary or human drug would be permitted for use.

What's Illegal?

Practitioners have to remember that even under AMDUCA, which allows for extralabel drug use, some drugs are absolutely off limits for use in food-producing animals. A list of drugs specifically prohibited from extralabel use as well as other pertinent information can be found at the Food and Drug Administration Center for Veterinary Medicine (FDACVM) website www.fda.gov/cvm/. Most of the drugs on the prohibited list are not approved for food animals. Some do have a food animal approval but can only be used according to the label. Drugs can be added to this list at any time, and it behooves all food animal practitioners to constantly monitor regulatory announcements for changes to drug use rules and regulations. Newsletters and publications from organizations such as the American Veterinary Medical Association (AVMA), American Association of Bovine Practitioners (AABP), American Association of Small Ruminant Practitioners (AASRP) and American Association of Swine Veterinarians (AASV), to name a few, alert practitioners to these changes.

Here are a few common situations that food animal practitioners deal with in relation to drugs prohibited for extralabel use. The first situation is the extralabel use of fluoroquinolones. Currently, fluoroquinolone products are labeled for use in beef cattle, dairy cattle < 20 months of age and swine for respiratory disease. This is the only approved use; any other use is prohibited. That includes another class of bovine, another food animal species or another indication. For example, use of fluoroquinolones to treat small ruminants with respiratory disease or calf diarrhea is prohibited.

The second situation is use of a prohibited drug in a "pet" food animal. In the eyes of the FDACVM, "pet" food animals do not exist. Thus, the extralabel use of prohibited drugs in the pot-bellied pig that lives in the house or the pet goat or steer, etc. is illegal, even if the owner guarantees it will never enter the food chain. Food animal practitioners are usually alert to this issue; however, our colleagues who have companion animal practices may not be. Since many of them have food animal companions presented to them, we must make them aware of these legalities.

Compounded and Counterfeit Drugs

A complete discussion of compounded and counterfeit drugs is beyond the scope of this article. Practitioners, however, should be aware that except for a few specific antidotes, the use of drugs compounded from bulk pharmaceutical ingredients in food animals is prohibited. Practitioners should be on the lookout for compounded and counterfeit drugs. If a drug is offered at a very discounted price, from an unknown distributor, and if it is unsolicited, it should be suspected to be a compounded or counterfeit drug. Drugs approved by the FDA will have either an NADA (original) or ANADA (generic) number. Counterfeit products may have labels almost identical to legitimate labels, including NADA or ANADA numbers and can be very difficult to spot. When in doubt, call the drug manufacturing company or the FDACVM.

Resources

The FDACVM and FARAD Web sites are very helpful. The "Green Book," which has all the FDA approved animal drug products, can be found at the FDACVM Web site. The FDACVM also publishes booklets on judicious use of antimicrobials in beef and dairy.