Earlier this week, BEEF Daily published an editorial in which I discussed several points I thought were worth considering when addressing antibiotic-resistant pathogens, and just who is responsible for creating them. One commenter quoted the oft-used figure that animal agriculture uses 80% of all antibiotics, and suggested we should cut back on our antibiotic use, particularly in growth promotion.
Is the commenter correct? Do we use 80% of all antibiotics, and are we overusing them or using them incorrectly? No. And yes. As I said in the editorial, antibiotic resistance is very complicated, which makes understanding the gulf between the “no” and the “yes” difficult yet critical if we’re to have an honest and ultimately successful conversation about antibiotic resistance.
The principal problem is that the Food and Drug Administration’s (FDA) figures on antibiotics are based on overall sales, not on use. While FDA is in the very early stages of addressing that problem, those are the only figures we have to work with at present. And sales figures tell you nothing about use or dosages.
When my doctor prescribes an antibiotic for me, he writes the prescription for an adult. When he prescribes an antibiotic for a child, he adjusts the dosage accordingly. I’m heavier than that child, and therefore need a considerably higher dose of antibiotic to treat my condition.
Likewise, when you treat a 1,300-lb. cow, you read the label and meter out the correct amount of antibiotic. Your cow weighs six times what I weigh, and 26 times what a 50-lb. child weighs; therefore, you will use considerably more antibiotic to treat her infection than is used to treat me.
The example above considers therapeutic use, which of course is only part of the debate. And the above example assumes you’re treating your cow with the same antibiotic that my doctor uses to treat me. And that’s where the 80% figure becomes confusing.
Consider these numbers from the FDA report titled “Antimicrobials Sold or Distributed for Use in Food-Producing Animals,” as discussed by Richard Raymond, an MD and former USDA under-secretary for food safety:
According to Raymond, ionophores account for 30% of the total amount of antibiotics sold and distributed in the U.S. Ionophores are only used in food animals; in fact, Raymond says if you use an ionophore to treat humans, it will make them very sick. Tetracyclines used in 2010 accounted for 41.5%, he says. Then there’s a list of drugs FDA is unable, by law, to report individually because it would disclose individual drug company information. That list totals 12% of all antibiotics, Raymond says, 10% of which are used exclusively in animal medicine.
“So 30% are ionophores and 10% are in the ‘not individually reported’ category and not used in human medicine,” Raymond says. Add 42% tetracyclines, and you now have 82% of all antibiotics used in animal medicine.
Raymond includes tetracyclines, which are also used in human medicine, because he says they’re not used much in human medicine, even though FDA considers them important in human medicine. Others disagree. Beyond that, Mike Apley, BEEF columnist and clinical veterinary pharmacologist at Kansas State University, says they’re an important part of the discussion because of the co-resistance problem.
The resistance genes for tetracyclines (about 1,200 identified to date, with three known mechanisms and one unknown mechanism) are often found on plasmids linked to the resistance genes for other compounds. So the use of tetracyclines may be linked to selection for resistance to other antibiotics as well, Apley says. He argues that animal agriculture bears the burden of confirming that in-feed and in-water use of tetracyclines are actually returning a benefit to animal health.
Thus, Apley says my argument that whether or not an antibiotic is used or not used in both human health and animal agriculture, at least where tetracyclines are concerned, is also short-sighted and misleading. I told you this was complicated.
So, with that in mind, consider this: Including tetracyclines in the discussion, it’s the remaining 18% where the conversation should focus, Raymond says. Carve out the tetracyclines, and the number jumps to 60%. Using the 18% figure, the main overlap is in macrolides, which are the drugs of choice in human medicine for treating campylobacter. While macrolides are used in cattle, most use in animal agriculture is in poultry and swine production.
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“The debate about the amount sold or used is just diversionary,” Raymond says. “It’s not the main issue in the public health debate about antibiotic resistance. The real issues are the judicious use of antimicrobials and is there a significant impact on human health?”
Apley agrees. “I accept that antimicrobial use in food animals can alter (antibiotic) susceptibility profiles (in pathogens),” he says. “But I also accept that there are multiple safe uses in agriculture for which the benefits far outweigh any risk. Our challenge in this conversation is to figure out which is which.”
For more on this topic, visit these resources:
- Richard Raymond, former USDA under-secretary for food safety, video
- NIAA symposium website
- FDA judicious use website
- FDA’s Federal Register notice on publication of Guidance 213
- Proposed VFD rule
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