03/19/2013 01:04 pm ET Updated May 18, 2013

Antibiotic Sales Data: A Tale of Two Medicines

Ever since FDA issued their 2010 report of animal antibiotic sales and also released a companion piece on human sales from a commercial interest named IMS, the claim has been trumpeted that 80% of all antibiotics are used in food animals. This conclusion was arrived at by comparing the roughly 13 million kilograms reported for animals with the 3.3 million kilograms reported by IMS for humans. Although FDA has warned that comparisons of these databases are inappropriate for numerous reasons, writers, bloggers, and anti-antibiotic advocates insist on repeating this non-scientific and meaningless statistic.

Now those same advocates are asking for more data to better understand the relationship between use in animals and the threat of antibiotic resistance in humans. But there are plenty of facts that can be gleaned from current data to promote such understanding.

While the total volume of antibiotics is higher in animals as might be expected from the sheer size of animal populations, the percentage of the various classes of antibiotics shows marked differences between animals and humans. The largest category of sales in animals is tetracyclines, at 43% of the total volume, and ionophores, at 29% of the total. Ionophores are not used at all in human medicine and thus have no potential contribution to human antibiotic resistance. And tetracyclines comprise only 4% of the total volume of sales for humans.

Conversely, penicillins are heavily relied on in human medicine, comprising 44% of the total sales, yet are only 7% of sales in animals. Furthermore, the next largest and important category of use in humans are cephalosporins, accounting for 15% while less than 1% is sold for animals. Fluoroquinolones account for 9% in humans and while not independently reported we know from previous industry data that this class represents less than 1% of the total antibiotic volumes sold in animals.

So, three compounds - penicillin, fluoroquinolones and cephalosporins - comprise 70% of the total sales for humans, while two different compounds - tetracyclines and ionophores -- comprise 70% of the total volumes sold for animals. The claim that the vast majority of the most "medically important" antibiotics are used in animals is not supported by the data.

Remarkably, an examination of the two most widely sold human antibiotics - penicillin and cephalosporins - shows that on a gross tonnage basis far more is sold for use in humans than for use in animals. While nearly 2 million kilograms are sold for human use, only about 900,000 kilograms are sold for animals. So a little over 300 million humans use more than twice as much as 10 billion food animals.

The lesson of this story is that the 80% "gospel" clearly paints an inaccurate and misleading picture and is meant only to scare not inform. When the data is analyzed a bit more closely it demonstrates the fallacy of jumping to conclusions about the actual risks to people from antibiotics used in food animals.