Off-Label Drug Use for Horses

Off-label drug use, which technically was illegal until recently, might be one of the most beneficial things we as vets

Off-label drug use, which technically was illegal until recently, might be one of the most beneficial things we as veterinarians do in the treatment of disease in animals. The technically illegal part was a result of the way a drug was licensed by the Food & Drug Administration (FDA) for use. For example, Drug X is licensed for the treatment of Disease Y, in a specific species, at a specific dosage, and at a specific frequency of administration. If there was deviation from that protocol (unless under special circumstances), then use of the drug technically was illegal.

This is an area not only where there have been changes in regulations over the past few years, but one that now can be influenced by clinical research. For example, the plain white penicillin (which is still a very good drug in the horse) is licensed for the use of treating infection at the dose of 3,000 International Units (IU) per pound of body weight. Clinical experience has shown that this "labeled" dose is too low to be effective in curing many infections and that the dose of 10,000 IU per pound is much more effective. The label still says 3,000, but most veterinarians use 10,000 because that”s what works. For a drug company to go back and complete all of the research necessary to put 10,000 IU on the label could cost several million dollars, so the drug is used in an off-label way most of the time.

This example carries through for many available drugs whose dose and frequency of administration are modified based on years of clinical research. That information is disseminated in veterinary journals, textbooks, at universities and conferences, and by word of mouth. The bottom line is that the little label on the bottle represents, at times, more than $10-$15 million and five to eight years worth of research (or more) to support the specific usage of a drug. After the research is completed, the drug”s performance must be evaluated on clinical cases.

Unfortunately, many of the decisions made by the pharmaceutical industry are based on financial considerations. This is in part due to the system of FDA checks and balances that is in place to ensure that a marketed drug does in fact do what it is claimed to do and is safe to use; the potential benefits of a drug must outweigh the potential side effects. One such factor is called the "therapeutic index." This is a value that approximates the "closeness" between a drug”s effective dosage and its toxic dosage–the greater the therapeutic index, the safer the

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Written by:

Michael A. Ball, DVM, completed an internship in medicine and surgery and an internship in anesthesia at the University of Georgia in 1994, a residency in internal medicine, and graduate work in pharmacology at Cornell University in 1997, and was on staff at Cornell before starting Early Winter Equine Medicine & Surgery located in Ithaca, New York. He was an FEI veterinarian and worked internationally with the United States Equestrian Team. He died in 2014.

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