Drug companies are driven by the need to produce profits for their stockholders. The cost of discovery and validation of new drugs for safety and efficacy is enormous, both in terms of money and time. For this reason, these companies are unwilling to make such an investment if a market big enough to justify the expenditures does not exist. While certain select veterinary drugs, such as ivermectin and carbrofen do create huge profits, many do not. The market for mouse analgesics, for example, is limited to research animals used in painful (usually surgical) protocols. Researchers with thousands of mice will not pay for expensive regimens. The market for tiger analgesics is considerably smaller, Food animal producers cannot pay $10 per daily dose for cutting edge antibiotics.
As of 1997, the number of companies doing animal health research on drugs in Canada had shrunk from 21 to 7. According to the Animal Health Institute in the United States, only 1 in 7500 compounds succeeds in gaining approval over a period of 10 to 12 years, at a cost of $250 000 000. Clearly drugs serving limited markets will not be forthcoming.
Veterinarians who wish to use only drugs approved for their particular species of interest thus face a huge obstacle; such drugs are rarely available. It is for this reason that legislatures have granted veterinarians the privilege of using drugs in an “off label” way; for example, in a manner that has not yet been approved for the species in question. Usually this means using human drugs in an animal species, but it may mean using a drug licensed for use in cattle in a pig or water buffalo, or licensed for use in dogs in a cat.
Such use is not just shooting in the dark. Safety and efficacy of human drugs are tested first in a number of animal species before clinical trials; if we can extrapolate from animals to humans, logic dictates that we can go in the other direction. In fact, when, in the mid-1980s, United States federal law mandated pain control for laboratory animals, such extrapolations were the basis for most analgesic use.
Furthermore, as we understand drug action in a clearer way, we can make reasonable extrapolations from established information. For example, we know that pain in pigs is not well-controlled by opiates, so the chances are that a new opiate will yield dubious results.
The point is that the alternative to extra-label drug use is doing nothing at all. The position of the Canadian Veterinary Medical Association (CVMA) on the extra-label use of drugs is to encourage Canadian veterinarians to prescribe veterinary approved drugs when available. The position states “the extra label use of drugs must be based on a valid veterinarian/client/patient relationship. Inherent with this is the responsibility to assure safe application to the animal and education of the client in a manner that will contribute to the safety and wholesomeness of foods of animal origin. Veterinarians can adhere to these principles through dedication to continuing education on pharmaceutical issues, and by obtaining the most up-to-date information from the pharmaceutical companies, veterinary colleges, and regulatory agencies” (1).
In the United States, the Animal Drug Use Clarification Act was passed in 1994. This law specifies that to use a drug in an off-label way, a veterinarian must have a valid veterinary/client relationship and not use the drug in animal feed. Certain drugs may not be used at all in food animals, for example, clenbuterol and chloramphenicol. Further, the Secretary of Health and Human Services may specify safe levels of residue for drugs used in food animals and require a method of detecting residues; proper labeling and record keeping are required by legislation based in 1997.
Some years ago, a number of veterinarians were cavalier about the use of antibiotics for growth promotion in feeds. This led Congress perilously close to banning extra-label drug use, which would have virtually destroyed veterinary medicine. Thus veterinarians should be careful not to violate the public trust in this area, lest a major tool be removed from them.