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U.S. Department of Health and Human Services

Animal & Veterinary

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Judicious Use of Antimicrobials for Aquatic Veterinarians

FDA Veterinarian Newsletter September/October 2005 Volume XX, No V

by Donald A. Prater, DVM, Leader, Aquaculture Drugs Team, Center for Veterinary Medicine

A new booklet describing principles of judicious use of antimicrobials for aquatic veterinarians was scheduled for release at the Aquaculture America meeting in Las Vegas, NV, in February 2006.

The booklet, Judicious Use of Antimicrobials for Aquatic Veterinarians, is a collaborative effort between the Aquatic Veterinary Medicine Committee of the American Veterinary Medical Association (AVMA) and the Aquaculture Working Group of the Food and Drug Administration’s Center for Veterinary Medicine (CVM).

The work is intended as a reference and educational resource for practitioners administering antimicrobials primarily to food fish, although the application of judicious and prudent use of antimicrobial drugs applies to the treatment of other types of aquatic animals, as well.

The booklet is the first guide produced for a minor species.

Currently, three antimicrobials are approved to treat various bacterial diseases in fish – oxytetracycline, sulfadimethoxine/ormetoprim, and florfenicol. All are administered as medicated feed. Oxytetracycline (Terramycin® 100 for Fish) and sulfadimethoxine/ormetoprim (Romet® 30) are approved for over-the-counter use.

In salmonids, Terramycin® 100 for Fish is approved to control ulcer disease caused by Haemophilus piscium, furunculosis caused by Aeromonas salmonicida, bacterial hemorrhagic septicemia caused by Aeromonas liquefaciens, and pseudomonas disease. This use has a 21-day withdrawal time. In catfish, it is approved to control bacterial hemorrhagic septicemia caused by Aeromonas liquefaciens and pseudomonas disease. This use has a 21-day withdrawal time. In lobsters, it is used to control gaffkemia caused by Aerococcus viridans, and this use has a 30-day withdrawal time.

Romet® 30 is approved to control furunculosis in salmonids (trout and salmon) caused by Aeromonas salmonicida. This use has a 42-day withdrawal time. In catfish, Romet® 30 is approved for the control of enteric septicemia of catfish caused by Edwardsiella ictaluri. It has a 3-day withdrawal time. The treatment regimen for both indications is 50 mg per kilogram of body weight for five consecutive days.

Under the Food and Drug Administration’s Compliance Policy Guide 615.115, “Extralabel Use of Medicated Feeds for Minor Species,” veterinarians may use oxytetracycline and sulfadimethoxine/ormetoprim to treat additional diseases or additional species, provided the medicated feed is produced in accordance with approved label directions. (The Compliance Policy Guide.)

In October 2005, florfenicol (Aquaflor®) was approved as a Veterinary Feed Directive (VFD) drug for the control of mortality in catfish due to enteric septicemia of catfish associated with Edwardsiella ictaluri. The treatment regimen for this indication is 10 consecutive days of therapy at a dose of 10 mg per kilogram of body weight. The withdrawal time is 12 days prior to harvest.

VFD drugs are available only upon the order of a licensed veterinarian. (Extralabel use of VFD drugs is strictly prohibited.)

VFD cate-gori-zation of Aquaflor® is consistent with CVM’s policy for approving new antimicrobials for use in medicated feeds. VFD status limits access to the antimicrobial and places it in the hands of prescribers with training and experience in the diagnosis and treatment of disease in populations of animals.

Judicious Use

The booklet describes concerns for the development of antimicrobial resistance and outlines principles for the use of antimicrobials in veterinary practice. The veterinary profession shares the concerns of the public, governmental agencies, and the public health community regarding the broad issue of antimicrobial resistance and specifically the risk of resistance developing in animals with subsequent transfer to humans.

In 1998, the AVMA started a profession-wide initiative, including companion and food animal practitioner groups, to develop and implement judicious use principles for the therapeutic use of antimicrobials by veterinarians. A general set of principles was approved emphasizing the need for veterinarians to strive to optimize therapeutic efficacy and minimize resistance to antimicrobials to protect public and animal health.

The 15 principles described in the new booklet are followed by a section discussing their application to large populations of fish, such as those treated in food fish aquaculture. Although veterinarians have not traditionally been the primary providers of health care to cultured fish species, the growing number and scale of cultured fish operations, in addition to backyard ponds and home aquaria, in the United States has resulted in the expanding involvement of veterinary practitioners.

The approval of the new antimicrobial, as a VFD drug, and the opportunity to utilize medicated feeds for minor species in an extralabel fashion has resulted in an important increase in the therapeutic options for aquatic veterinarians. This increase in therapeutic options is accompanied by an increased responsibility for judicious use of antimicrobials. The new booklet will be a substantial resource for these practitioners.
For a copy of the booklet, contact Dr. David Scarfe, Assistant Director, Scientific Activities Division at the American Veterinary Medical Association, 1931 N. Meacham Rd., Suite 100, Schaumburg, IL 60173; Direct phone – (847) 285-6634; (800) 248-2862 Ext 6634; Dscarfe@AVMA.org. Or contact the Communications Staff, FDA/Center for Veterinary Medicine, 7519 Standish Place, HFV-12, Rockville, MD 20855; 240-276-9300.