Adding up antimicrobial use

On Feb 14 the Animal Health Institute, representing companies that manufacture animal health products, reported that 20.5 million pounds of antimicrobials were sold for use in animals in 1999. The figures, up from 17.8 million pounds in 1998, were based on purchase information from manufacturers and member companies.

AHI President and CEO Alexander S. Mathews said that the majority of antimicrobials continue to be used for treating and preventing disease, and use of the drugs goes "a long way in promoting animal health, food safety, and food security."

Of the 20.5 million pounds used in 1999, AHI reported 17.7 million pounds were used for treatment and prevention of disease, and 2.8 million pounds were used for growth promotion.

This number is thought to be underestimated by the Union of Concerned Scientists, a national alliance of citizens and scientists, whose figures added up to 26.4 million pounds used.

The differences lie in both groups' definitions of therapeutic and nontherapeutic antimicrobials.

The AVMA's Steering Committee on Judicious Anitmicrobial Resistance defines a therapeutic antimicrobial as those used for the "treatment, control, and prevention of bacterial disease." This is the same definition used by the AHI. The UCS defines therapeutic antimicrobials as those used for the treatment of disease in animals only.

The UCS's own report, "Hogging It," released on Jan 8, states that American livestock producers use 26.4 million pounds of antimicrobials just for the nontherapeutic purposes of growth promotion and disease prevention. The authors of the report state the estimate is based on publicly available information including herd size, approved drug lists, and dosages.

The authors of "Hogging It" report that their findings include only nontherapeutic usage in the three major livestock sectors of cattle, swine, and poultry. AHI's covers all uses, therapeutic and nontherapeutic (growth promoting, according to AHI) in all animals. The UCS indicated that their figures in the nontherapeutic category alone surpass AHI's estimates by almost 50 percent.

As use of antimicrobials is increasing year after year, and concerns as to how those antimicrobials are used, UCS's major concern is that, according to their report, roughly 70 percent of these antimicrobials are being given to already-healthy livestock.

"Mostly, we want to preserve these antimicrobials for sick animals and sick people," said Jane Rissler, senior staff scientist of the Food and Environment Program of UCS.

AHI's report of increasing usage is attributed greatly to the sale of ionophores and arsenicals, which increased 2.5 million pounds from 1998 to 1999. These classes of antimicrobials have no application or connection to human medicine.

"The FDA approved these products on the grounds that these products are safe and effective, and they're valuable veterinary tools," said Matt Baun, director of public affairs at AHI. "To remove these tools without scientific justification is a dangerous precedent to be setting. Until the signs show that these products are no longer safe, it doesn't matter how many pounds were used."

David M. Bell, MD, antimicrobial resistance coordinator for the Centers for Disease Control and Prevention, said that concentration on mere estimates from a variety of sources should prompt the need for an accurate monitoring system.

"At some level I'm concerned that too much attention is focused on what the percentages are in agriculture versus human use, and then there are people who disagree what those numbers are," Dr. Bell said. "These are estimates, and they are all over the map.

"The percent of antimicrobial use in agriculture might be interesting as background information, but I think the really important thing is to develop a system for ongoing monitoring so that we can assess the impact and, if necessary, work with the professional groups and agricultural community to take appropriate preventative measures, rather than argue about what the percents are."

"It's a top priority in our Public Health Action plan, to combat antimicrobial resistance," Dr. Bell said. "The FDA, CDC, and USDA are in discussion about how to do that. There are various projects under way."