Companies that make antibiotics for use in farm animals have already agreed to remove growth-promotion indications from their products labels by the end of this year, but a new report claims that a large number of veterinary drugs that are also medically important to humans will still have labels that do little to curb the overuse of antibiotics on livestock.

This is according to a new study by the Pew Charitable Trusts, which looked at the nearly 400 antibiotics made for farm animals that are also deemed vital for protecting human health, and found that around one-third of these drugs will continue to have questionable labeling and direction even after they stop remove claims that the antibiotic will promote growth in the animals that take it.

Antibiotics provided to livestock — typically put into their feed for water — account for around three-quarters of all antibiotics sold in the U.S. For decades, the drugs could be used openly and without any prescription for growth-promotion.

In late 2013, the FDA announced voluntary industry guidance, calling on drug companies to remove approvals for growth-promotion. However, that only only affected a small number of drugs and allowed farmers to continue using the same amount of these drugs under the guise of “disease prevention,” even though a number of veterinary scientists contend that continual, low-dose prophylactic use of these antibiotics only encourages the development drug-resistant pathogens.

A recent report commissioned by the UK Prime Minister noted that many of the antibiotics consumed by farm animals pass through their digestive systems without being metabolized, meaning these drugs can enter into the soil and the ground water. A study out of China showed that sub-therapeutic use of antibiotics in pig farming resulted in huge increases in the number of antibiotic resistance genes found in the area, when compared to an antibiotic-free site in a similar region.

In order to rein in this sort of potentially dangerous overuse, public health advocates have called for requirements for drug labels that promote judicious use of these drugs: limiting the duration of use, accurate dosing information, and clearly specified indications for use.

While the majority of the medically important drugs will now have labels that meet those criteria, more than 140 of them will not, according to the Pew report. Making things more problematic, note the researchers, is the fact that a large number of these questionably labeled drugs are brand-name or patented drugs, meaning there are few (if any) available alternatives.

Prolonged constant exposure to a single antibiotic can be an open invite to drug resistance, and many of these drugs do provide recommended limits on the duration of use (often no more than three weeks). But according to the study, around 30% of labels for these medically important drugs have open-ended, vague, or prolonged (up to six weeks) duration recommendations. For example, some antibiotics say to administer during the ill-defined “times of stress.”

Speaking of “times of stress,” that’s one of the non-specific indications that drug makers are employing in their labels to guide the use of their drugs.

According to the Pew survey, dozens of antibiotics have labels listing unclear or problematic indications. Twenty-three of the antibiotics still reference “maintenance of weight gain” as an indication, even though that’s a non-medical production outcome. Seven drugs say they are for prevention of “early mortality,” but don’t mention what disease they are preventing that would otherwise cause that death.

A large of chunk of these drug labels reference indications that arguably shouldn’t need antibiotics for treatment. The report gives the example of 46 labels that include indications related to reducing the prevalence of liver abscesses in cattle.

While that sounds like something you probably want medicine to treat, Pew counters that these abscesses are typically caused by the amount of grain fed to the cattle.

“In this case, antibiotic use is not primarily directed at ensuring the health and well-being of the animal but at reducing economic losses caused by liver condemnation at slaughter, which means the liver cannot be sold for human consumption,” reads the report.

When you get an antibiotic from your doctor, the pills are usually manufactured so that one pill equals one dose, and the label has specific details on how many and when to take the drug. Things aren’t always so clear on the farm, notes the Pew report.

The study found that 25% of medically important antibiotics that are provided to animals through their feed or drinking water “do not specify a narrowly defined dosage directly connected to the animal’s weight.” Dozens of additional drugs have what Pew describes as “excessively wide” dosage ranges.

The report concedes that it’s not always feasible to provide farmers with narrow, weight-based dosing ranges, but argues that these should be rare cases.

“[L]abels that do not specify dosage based on an animal’s weight or provide for an inordinately wide dosage range should be critically reviewed to ensure they are consistent with FDA criteria for judicious use,” reads the report, which calls on the FDA to do more to promote judicious labeling of these drugs.

“FDA has publicly committed to ensuring that labels follow the judicious use of antibiotics in food animals, in particular with respect to establishing appropriate durations of use,” conclude the Pew researchers. “The agency should go further and announce a concrete plan and timeline for making all label revision changes — regarding duration limits and other aspects of appropriate use — as quickly as possible and follow through accordingly.”

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