Two weeks ago, I broke the news of a new FDA report that estimated for the first time the amount of antibiotics sold in the United States every year for use in agriculture: 28.8 million pounds.

That long-awaited report didn't answer a crucial question: What volume of antibiotics are sold in the United States each year for human use. It's a crucial question because, in answer to concerns about antibiotic resistance arising on farms, the answer has always been that human medicine is equally culpable because it uses similar volumes of antibiotics.

The only research that has attempted to answer that question is contained in a decade-old report by the Union of Concerned Scientists that put the proportion of antibiotics going to animals at 70 percent of the U.S. total.

That UCS report and estimate are a decade old not because no one has cared about the topic, but because accurate updated figures have been so hard to get. So we owe a special holiday thank-you to the researchers at the Center for a Livable Future, who decided the release of the FDA report justified another attempt to get the numbers straight. They succeeded.

The proportion of antibiotics sold in the United States each year that go to animals turns out to be not 70 percent, but rather 80 percent. Here's CLF's Ralph Loglisci, who got the confirmatory numbers from the FDA:

In accordance with a 2008 amendment to the Animal Drug User Fee Act, for the first time the FDA released last week an annual amount of antimicrobial drugs sold and distributed for use in food animals. The grand total for 2009 is 13.1 million kilograms or 28.8 million pounds. I ... contacted the FDA for an estimate of the volume of antibiotics sold for human use in 2009. This is what a spokesperson told me: "Our Office of Surveillance and Epidemiology just finished an analysis based on IMS Health data. Sales data in kilograms sold for selected antibacterial drugs were obtained as a surrogate of human antibacterial drug use in the U.S. market. Approximately 3.3 million kilograms of antibacterial drugs were sold in year 2009. OSE states that all data in this analysis have been cleared for public use by IMS Health, IMS National Sales Perspectives™." 3.3 million kilograms is a little over 7 million pounds. As far as I can determine, this is the first time the FDA has made data on estimates of human usage public.

At its blog, CLF lays out the math for each major drug class as sold for animal use and human use, with a long discussion of the significance of the different drug classes. Here's the CLF table summing up the math, but please go over to CLF's blog for its discussion.

Most important to note: Most of the drugs used in animal agriculture and in human medicine are functionally identical. That's one reason why the overuse of antibiotics in animals is such a concern: When organisms become resistant on the farm to drugs used on livestock, they are becoming resistant to the exact same drugs used in humans. (One major drug category used in animals, ionophores, do not have a direct human analog. But use of them on farms is still a concern, because resistance factors can move freely between species of bacteria. That's a discussion for another day.)

Loglisci's conclusion is also worth underlining:

The next battle, which industry has already begun, is defining what non-therapeutic use will constitute. Producers are already claiming that the use of antibiotics for growth promotion has decreased, maintaining current low-dose usage is aimed at disease prevention. Regardless, all low-dose usage of antibiotics can lead to a significant increase in antibiotic resistance.

Image: Flickr/Epsos