When looking at how antimicrobials are used in animals and humans, it’s important to carefully look at the differences between the groups.

Speaking to more than 170 participants at the National Institute for Animal Agriculture’s 2012 Antibiotic Symposium in Columbus, Ohio this week, Ron DeHaven, DVM, MS, American Veterinary Medical Association (AVMA) executive vice president, broke antibiotic use into three categories.

For companion animals, DeHaven explained that most antimicrobial use is exclusively under a veterinary-client-patient relationship.

In food animals, some antibiotics can be used over-the-counter as per their approved labels, in feed or water, or added by a feed mill or producer to feed as directed by the FDA on the label. Antibiotics for food animals can also be used under the Veterinary Feed Directive (VFD) and are prescription only (currently only florfenicol and tilmicosin are approved for this use). DeHaven noted that OTC medically-important antimicrobials may also be moved under a VFD designation.

The third use for food animals is under a prescription by a veterinarian.

Differences in human/food-animal use

In humans, antimicrobials can be used for treatment or prevention, and the physician determines the indication, route, dose, frequency and duration. “There are no restrictions on extralabel or off-label use of human antimicrobials,” DeHaven said.

In food animals, however, only drugs approved for specific indications, and under specific dose, duration, frequency and route of administration can be used, and extralabel uses are heavily regulated.

Controversy and complexity

DeHaven noted that one of the concerns is the reservoir or source of antimicrobial resistance. “There is no clear scientific evidence of how and to what extent such exposure of antimicrobial resistant pathogens affects human health,” he said. “There is no hard evidence that connects human infection with resistant bacteria caused by use of antimicrobials in food animals. There is no evidence that restricting or limiting antimicrobial use in food animals will improve human health or reduce the risk of antimicrobial resistance.”

Benefits vs. risk

We use antimicrobials in food animals because of the numerous benefits to human and animal health. Antimicrobial use improves animal welfare by preventing, controlling and treating disease. It enhances food safety because “Healthy animals produce safer food,” DeHaven said.

What are the disadvantages? Antimicrobial resistant bacteria can develop.

So what is the preferred use to keep the benefits and curtail resistance? Less use vs. more use, lower doses in more animals, higher doses in fewer animals, stronger drugs or culling more animals? These are the questions that are being dealt with today, DeHaven said.

There are different camps that propose different approaches. One is to discontinue the use of antimicrobials in food animals. “Don’t take chances, eliminate or reduce the use of antibiotics in animals on the possibility it is jeopardizing human health,” DeHaven said. “Or, continue use and do not take action unless there is a scientific risk assessment. The benefits to animal health, welfare and food safety outweigh the risks to human health based on risk assessments which are minimal.” The question is if there is a novel approach somewhere in the middle.

AVMA’s position on antimicrobials

DeHaven stated that the AVMA supports the judicious use of antimicrobials in food animals to maximize benefits and minimize the risks for resistance. “We support greater veterinary involvement in any use of antimicrobials. Actions to limit use should be based on available scientific research and risk-based assessments.”

The AVMA also does not support the Preservation of Antibiotics for Medical Treatment Act (PAMTA) legislation. “It lacks risk-based assessment,” he said. “It has the potential to eliminate two or three of the four approved uses of antibiotics in animals, and there could be animal welfare implications with more disease if antibiotic use is restricted.”

AVMA believes there should be – and will be – greater veterinary oversight of antibiotic use. The VFD is the primary vehicle for greater oversight of antimicrobials in feed, but the degree of oversight should be proportionate to the risk.” To look at this issue, AVMA has put in place a Veterinary Oversight Steering Committee.

DeHaven says the AVMA would prefer there be regulation vs. legislation when it comes to antimicrobial use in food animals. “With legislation there is less opportunity for scientific input and evaluation, and it tends to be politically motivated,” he said. “Regulation involves rulemaking that provides months or years for input. It is more deliberative, and statutory authority already exists.”