Vet Column 5-31-10 | TheFencePost.com

Vet Column 5-31-10

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

In the last several years, new antibiotics and other injectable products for animal use have been brought to market and producers have access to more choices than before. Many have extended duration of therapeutic effect and are more expensive, sometimes interpreted as being more powerful. A recent publication by authors from Kansas State University and the University of Nebraska reviewed the Food and Drug Administration (FDA) guidelines for use of FDA-approved medications in animals.

FDA approves drug labels with specific disease indications, animal classes, routes of administration, durations of therapy and doses. Deviation from these label inclusions could potentially cause lack of effectiveness for the disease being treated, toxicity to the animals, or a violative residue in food harvested from the animal. FDA establishes a withdrawal time based upon the dose, anatomical location of administration, route, frequency, and duration regimen approved on the label.

Prior to the Animal Medicinal Drug Use Clarification Act (AMDUCA) regulations in 1996, it was illegal to use a drug in an extralabel manner (manner other than specified on the label). This law and resulting regulations enabled licensed veterinarians to adjust the use (extralabel drug use (ELDU)) of an FDA-approved drug other than as labeled when the health and well-being of that animal or group of animals is threatened.

Extralabel drug use shall not be considered if the purpose is for growth promotion, reproductive performance, or alteration of cost of therapy. Most importantly, however, is that even if the rationale for ELDU is reasonable, ELDU must not lead to a violative drug residue. Additionally, AMDUCA does not allow for ELDU of medicated feeds.

In order to prevent unwanted consequences from ELDU, ELDU can only be used when a “valid veterinary-client-patient-relationship” (VCPR) has been established and the ELDU is considered by the veterinarian. A valid VCPR exists when, 1) the licensed veterinarian has assumed clinical responsibility for the animals and the owner of the animals has agreed to follow the veterinarian’s instructions, 2) the veterinarian has sufficient direct knowledge of the animal’s condition and their care, and, 3) the veterinarian is available for follow-up evaluation.

Additional conditions must be met before ELDU may be legally considered. A careful diagnosis is made by an attending veterinarian; there is no marketable drug specifically labeled to treat the condition diagnosed; the treatment at the dosage recommended by the labeling was found clinically ineffective; assurance that identity of the treated animal(s) is carefully maintained; and a significantly extended drug withdrawal is assigned to the animal(s) so that no violative residue occurs. If the individual animal cannot be identified for the extended withdrawal time, then the extended withdrawal time must be applied to the entire group.

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Three quick examples of ELDU of injectable drugs that can cause violative residues include use of penicillin G at doses greater than the label dose of 1 cc per hundred pounds of body weight; administering Excede by an unapproved route; and administering flunixin meglumine (Banamine) by an unapproved route. Excede administered subcutaneously in the neck region instead of the label-directed middle portion of the back of the ear or base of ear locations changes the disposition of the drug. The potential for a violative residue at the injection site increases the required withdrawal time well beyond the label withdrawal time of 13 days.

Administering Banamine by subcutaneous or intramuscular routes because of convenience to avoid the intravenous approved route causes a great deal of tissue damage at the injection site and violative residues have been documented by the FDA to occur in cattle beyond the four day withdrawal time the FDA requires for intravenous use of the medication.