The U.S. Food and Drug Administration (FDA) is tightening up regulations on the marketing and labeling of so-called “medically important antimicrobials” used on food animals. Such a move has long been sought by those concerned about how overuse of such drugs can lead to antibiotic resistance and threaten public health. In recent weeks, the antibiotic-resistant “superbug” known as mcr-1 has been detected in two people and two pigs in the U.S., causing renewed alarm about resistance in general and ways to combat it. a letter to animal drug distributors, FDA’s Center for Veterinary Medicine reminded retailers that the marketing status of such drugs will change on Jan. 1, 2017, from over-the-counter to requiring either a prescription (Rx) or a veterinary feed directive (VFD). The agency signaled this move in December 2013 with the publication of Guidance #213. The document called on sponsors of approved medically important antimicrobials administered to animals through medicated feed or water to voluntarily remove from their product labels any indications for use related to growth promotion. FDA noted that all affected drug sponsors committed to making the changes the agency requested within the suggested timeframe. “In some cases, drug sponsors may choose to withdraw a product approval completely. Drugs that have either an Rx or VFD marketing status can only be prescribed or authorized for use in animals by a licensed veterinarian,” the letter continued. “Distributors that are unable to meet the applicable State and Federal requirements for selling and distributing Rx and VFD animal drugs may no longer be able to sell these products once they have transitioned to their new marketing status. If this is the situation, distributors may need to return their unsold inventory to the manufacturer or wholesaler.” These changes comes on the heels of news that U.S. Department of Agriculture scientists have twice this year detected antibiotic-resistant E. coli in pig intestines. The first sample was from a slaughterhouse in South Carolina and the second was from a slaughterhouse in Illinois. Government officials recently said the first human and animal cases of the same gene, mcr-1, was identified in May in an E. coli strain from a woman in Pennsylvania who had not recently been outside the country. In a May 26 report, the Center for Infectious Disease Research and Policy (CIDRAP) detailed the actions of the Department of Health and Human Services (HHS).

“Beginning this fall, the CDC’s antibiotic resistance lab network will provide the infrastructure and lab capacity for seven to eight regional labs, as well as labs in all states and seven major cities and territories, to detect and respond to resistant organisms recovered from human samples,” CIDRAP reported.

The Pennsylvania woman appears to be recovering, but a second human case and the second case in a pig confirmed in recent days have health officials concerned about transmission routes. The second swine case turned up in a pig at an Illinois slaughterhouse, USDA reported in mid-June. The second human case was detected in a person in New York a month after the case in Pennsylvania was diagnosed, according to Antimicrobial Agents and Chemotherapy, a journal of the American Society for Microbiology. According to the journal, the finding in New York was part of a global effort called the SENTRY Antimicrobial Surveillance Program, which tested more than 20,000 patients from around the world with E. coli or Klebsiella pneumoniae strains. Of those 20,000 patients, 390, or about 1.9 percent, were resistant to colistin and 19 of those 390 tested positive for the mcr-1 gene. In both U.S. cases, while the individuals carried the superbug gene that is resistant to colistin, they were susceptible to other antibiotics, which made the infections treatable. (To sign up for a free subscription to Food Safety News, click here.)