Big news in the realm of agricultural antibiotics: For the first time in almost 37 years of trying, the US Food and Drug Administration has achieved some control over the meat-industry practice of routinely giving antibiotics to livestock. The drawback: The control comes in the form of a voluntary commitment by veterinary drug manufacturers – and while the FDA maintains the voluntary program will work, there is widespread skepticism that the agency may be optimistic.

Here is what has happened; it takes a few steps to lay out. The FDA has been putting this voluntary program together for several years now, via two "Guidances" (numbered 209 and 213), which are nonbinding agency recommendations without the legal force of regulations, plus a Directive, which fills in the details. The three documents set forth what the agency wants to see happen: for meat production to stop using the routine micro-doses ("growth promoters" or "subtherapeutic antibiotics") that fatten animals, but create antibiotic resistance; for farmers to stop administering antibiotics to entire herds or flocks via their feed and water; and for antibiotics to be used on farms only with the oversight of a licensed veterinarian. They accomplish that by asking veterinary antibiotics manufacturers to change the labeling on the drugs, so that they can no longer legally be sold over-the-counter to be used for growth promotion. The first Guidance, 209, was made final a year ago, and sets out the rationale for making this change. The second, 213, was made final last December; at that time, the FDA gave veterinary drug manufacturers three months to say whether they were going to comply.

Which brings us to the new news: On Wednesday afternoon, the FDA's Center for Veterinary Medicine published the list of veterinary drug manufacturers who have agreed to comply with the voluntary label change. Out of 26 manufacturers in that market, 25 agreed to cooperate. The FDA says this represents "99.6 percent of the applications," that is, drugs and the ways they are administered.

So: Is the long battle over growth-promoter antibiotics, banned in Europe for 8 years now, over just like that? Or is there more to do?

Here's where the skepticism comes in. There are some important caveats.

The voluntary program covers only "medically important" antibiotics, that is, ones which are functionally identical to drugs that are crucial in human medicine. The public discourse over ag antibiotic use over the past few years has demonstrated that meat-industry interests and human medicine disagree over what "important" means – for instance, the National Pork Producers Council dismisses tetracycline as being "rarely used" in human medicine, but physicians who use it consider it a vital drug that they do not want to lose to resistance.

The voluntary program addresses only growth-promoter uses, but not the middle category of drug use (that is, not fattening, but also not disease treatment) known as "prevention and control." Advocates for restricting antibiotic use fear that the current uses will simply be redefined into the next category. There are precedents in other countries that earlier attempted bans to make that fearseem reasonable, and in the US, major veterinary-drug manufacturer Zoetis has said that they do not expect their sales numbers to change.

And finally, the FDA does not currently receive from the manufacturers any data which would allow it to know whether the voluntary ban is working or not. The only data given to the government about antibiotic use in animals (under a law with the acronym ADUFA) reports only gross sales by weight in each family of drug. Which route of administration, which intention, which species it is being given to – none of that is collected. So the FDA lacks a crucial enforcement tool.

By coincidence, Michael Taylor, the FDA's deputy commissioner for foods, spoke to my MIT fellowship class the day before the list was published. I asked him about what he expected. Here's what he said:

The thing to zero in on is, how do we get the data to verify the remaining uses of these drugs are being disciplined, as our policy says they should be, and limited to use in a very targeted way under veterinary supervision, and to verify there are actually reductions in antimicrobial resistance resulting from this? There are a number of policy issues around our ability to get that data... We think we are on a positive pathway, but there is a lot of work remaining to be done. ... The question about which there is a lot of continued skepticism and concern is, how will we at FDA police the remaining prevention uses and how will we document them to be sure they are disciplined. We are going through a rulemaking to see how far under current law we can push the companies to provide data, and also working with (the US Department of Agriculture)... If we can't get what we need through those means, we won't hesitate to flag that there is a legislative need here. We need to leave no stone unturned to get the data to demonstrate that we know what is happening.

Here are some early reactions, from advocates who have been working on this issue, to the company commitments.

Laura Rogers, the Pew Charitable Trusts: “The FDA and drug makers appear to have passed the first big test of the agency’s voluntary approach. This is very encouraging – as is the agency’s transparency in reporting this information today – but there’s a lot more to do... The agency needs this information to calculate the ultimate measure of success—declines in non-therapeutic antibiotic use and fewer resistant infections in animals and people.”

Steve Roach, Keep Antibiotics Working : "We remain skeptical that FDA’s approach will do much to mitigate the public health threat caused by antibiotic resistance. These letters submitted by the drug companies are not binding, so the companies can still stop participating at any time. Even more important, FDA has done nothing to limit the continued use of antibiotics for routine disease prevention. In terms of dose, duration, and number of animals the drug is being administered to, this type of use can be identical to growth promotion, which the FDA is asking the companies to phase out... Getting the companies to send letters is the easy part, actually reducing antibiotic overuse is the real challenge."