Practitioners have to remember that even under AMDUCA, which allows for extra-label drug use, some drugs are absolutely off
limits for use in food producing animals. A list of drugs specifically prohibited from extra-label use as well as other pertinent
information can be found at the Food and Drug Administration Center for Veterinary Medicine (FDA/CVM) Web site
http://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, will alert practitioners
to these changes.
In the field
Here are a few common situations that food animal practitioners deal with in relation to drugs prohibited for extra-label
use. The first situation is the extra-label use of fluoroquinolones. Currently, there are fluoroquinolone products labeled
for use in beef cattle for respiratory disease. This is the only approved use, and any other use is prohibited. That includes
another class of bovine, another food animal species or another indication. So, for example, use of fluoroquinolones to treat
dairy cattle with respiratory disease, small ruminants with respiratory disease or calf diarrhea is prohibited.
The second scenario is use of a prohibited drug in a food animal species that is more of a pet. In the eyes of the FDA/CVM,
pet food animals do not exist. So extra-label use of prohibited drugs in the pot-bellied pig that lives in the house, as well
as a pet goat or steer, etc., 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. And as many of them have food animal companions presented
to them, we must make them aware of these legalities.
Case in point
A common situation food animal practitioners face in relation to the constraints of extra-label use under AMDUCA is the need
for a non-steroidal anti-inflammatory drug for endotoxemia in a beef animal. Flunixin meglumine is approved for use in cattle
for endotoxemia and is highly effective. Phenylbutazone is not prohibited for use in beef animals, but it has no label approval
for any indication in food animals. So even if phenylbutazone is deemed equally effective for the endotoxemia and is most
likely cheaper, it is not permitted for use in this situation.
If however, a case of chronic osteoarthritis presents in a beef animal, and the veterinarian considers phenylbutazone to be
superior to flunixin meglumine therapeutically, it can be selected as long as adequate withdrawal times are established. Because
of the very long half-life of phenylbutazone in cattle, one dose of phenylbutazone can lead to violative residues for months.
So, it is an acceptable choice for a valuable breeding animal that's value is not in its carcass. It is not an acceptable
choice in a feeder or veal calf that will go to slaughter.
So for any extra-label use, it is imperative to know what the withdrawal time should be, and any other pertinent pharmacological
information before administering a drug. Phenylbutazone is also prohibited for extra-label use in female dairy cattle 20 months
of age and older, so it cannot be used in this class of animal for any reason.
Compounded and counterfeit drugs
A complete discussion of compounded and counterfeit drugs is beyond the scope of this article. However, practitioners should
be aware that except for a few specific antidotes, the use of compounded drugs in food animals is prohibited.
Practitioners should be on the lookout for compounded and counterfeit drugs on farms. 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 FDA/CVM.
Dr. Navarre works as an extension veterinarian with Louisiana State University's Department of Veterinary Science.