Does too much drug use cause drug-resistant organisms?

By Robert Tremblay

Last fall, a in forum a Toronto conference discussed the use of antibiotics and other antimicrobial drugs in livestock production.

The conference wanted a forum for stakeholders in animal agriculture to look at the broader issue of antimicrobial resistance (AMR). Antimicrobial resistance describes the situation where our antimicrobial drugs lose their ability to either kill or slow the growth of the bacteria and similar microbes that cause illness both in humans and animals. Some very vocal activists accuse the livestock food production industry of fostering antimicrobial resistance through irresponsible use of these drugs.

It has proven to be very difficult to draw a direct line between antimicrobial use in livestock production and the emergence of AMR to drugs used to treat human diseases. Several studies in western Canadian feedlots have either failed to find evidence of widespread AMR or failed to find AMR at all. Even in the absence of evidence for a direct link, European Union countries have already decided to exercise the precautionary principle and are limiting the types of situations where antimicrobial drugs can be used in livestock production. For example, they prohibit routine use for enhancing production efficiency.

The U.S. Food and Drug Administration (FDA) has also taken action to try to control the use of antimicrobial drugs in livestock where those drugs are also important for use in humans. In the past few years, they have implemented special controls over the use of drugs they find especially useful in human medicine. One group of important drugs is the fluoroquinolone group of drugs. When one of these drugs, enrofloxacin (this is known as Baytril) was approved for use in food-producing animals, the FDA imposed restrictions on how it could be used. They hoped to encourage its use in situations where other drugs had been used first. The Canadian regulators also emphasized this type of use.

This month, the FDA issued another directive to restrict the use of another class of antimicrobial drugs that also has great value in treating people. This second group is the cephalosporins, particularly, the more recently developed cephalosporin drugs. Ceftiofur, the active ingredient in the Excenel and Spectromast products, is one of the drugs that the FDA would like to better control.

They are especially interested in reducing the use of these drugs in circumstances where they have not been clearly shown to be effective; in other words, in situations other than those described on the product’s label. If those same drugs are used in any manner differently than from what is stated on the label, there may not be any acceptable research to support that different use.

So far this new directive is not fully implemented, but by issuing the directive the FDA has implied that it is serious about controlling the use of cephalosporin drugs. Even when the directive becomes fully effective, it will not apply to Canadian veterinarians or farmers. Health Canada is responsible for drug use regulations here. It is important to consider whether we can learn from the concerns in the United States.