The WHO has released a first-ever list of 21 antimicrobials earmarked as “authorized for use in humans only” – a first for the organization in its efforts to protect overuse and abuse of critical first-line drugs that need to be protected by overuse in animal and plant health sectors – and consequent antimicrobial resistance (AMR). 

Significantly, most of the 21 antimicrobials earmarked by  WHO as “authorized for use in humans only” include mostly novel compounds developed and authorized over the past six years. 

The category “mainly contains newer antimicrobials that are very important in treating serious multidrug-resistant infections in humans,” WHO explains in its guidance. So the new WHO label is effectively a warning sign to the farm industry that they should not be used in animals or plants in the future. 

Among the antimicrobials authorized “for use in humans only” are: plazomicin, aminomethylcycline, anti-pseudomonal penicillins with and without β-lactamase inhibitors, carbapenems with or without inhibitors, third- and fourth-generation cephalosporins with β-lactamase inhibitors, sulfones, as well as drugs critical to treating tuberculosis and other mycobacterial diseases.

Some of the older ones on the WHO list, e.g. carbapenems, are not licensed for use in animals in the United States, but are sometimes used in companion animals. 

The report aims to provide guidance for authorities in the public health and animal health sectors, veterinarians, prescribers of antimicrobials, and agricultural professionals, as well as classify antimicrobial categories by importance to human use, WHO said.   

Reducing risks to human health 

A second category of medically important antimicrobials refers to drugs “authorized for use in both humans and animals.” 

But this is further broken down into “highest priority critically important antimicrobials (HPCIA),” “critically important antimicrobials (CIA),” “highly important antimicrobials,” and “important antimicrobials.” 

Widespread animal use of leading antibiotics has become a major driver of growing ‘superbug’ resistance to common drug treatments, or AMR. In 2019 AMR was associated with the deaths of close to 5 million people globally. 

To address these risks, the use of critical antimicrobials needs to be rationalized more systematically in both animal as well as human health. WHO’s drug classifications create an order of priority for doing this, notes an analysis from the University of Minnesota-based Center for Infectious Disease Research and Policy (CIDRAP.) 

“The risk to human health is greatest if the antimicrobials listed as ‘authorized for use in humans only’ are used in non-human sectors,” noted the CIDRAP analysis. “Those risks and impacts decline progressively with the use of agents from the other categories.”

“For instance, the criteria for inclusion in the first two medically important antimicrobial categories is whether the antimicrobial class is one of the limited available therapies or the sole available therapy to treat serious bacterial infections and if it’s used to treat bacterial infections possibly transmitted from non-human sources (such as Salmonella and Escherichia coli).

“Among the classes categorized as HPCIA are third- and fourth-generation cephalosporins, quinolones, and polymyxins. The CIA category includes aminoglycosides and macrolides,” CIDRAP noted. 

Scale of prioritization of medically important antimicrobials (MIA)

A One Health approach

The non-human use of antimicrobials in fact includes a broad range of species, beyond the historical focus on food-producing animals. These include aquaculture, companion animals, and fur-bearing animals. Reducing antimicrobial use in the non-human sector remains vital for preserving the efficacy of these substances, WHO said. 

Antimicrobial resistance (AMR) occurs when pathogens like bacteria, viruses, fungi, and parasites no longer respond to antimicrobial medicines, making infections harder to treat while increasing the risk of disease spread, severe illness, and death. Infections typically treated with routine medicines thus become life threatening. 

“Because AMR develops and transfers within and among all sectors, minimizing the risk of emergence and transmission of AMR  calls for a One Health approach,” WHO explained in the new guidance.

“To improve the responsible and prudent use of antimicrobial agents—and in particular medically important antimicrobial agents—it is thus essential to decrease their inappropriate use across sectors.”

Additionally, the report advocates for the more systematic inclusion of medically important antimicrobials in AMR monitoring and surveillance programs – which continue to be patchy and incomplete in most countries of the world.

New WHO category ‘for use in animals only’

In addition to the existing “highly important antimicrobials” (HIA) and “important antimicrobials” (IA) classifications, the WHO now includes an “authorized for use in animals only.” This group was added to “ensure that all antimicrobials used in animals come under scrutiny as part of the standard evaluation approach, so that they would not be placed in a low priority category by default, without proper assessment of the potential risk of AMR in humans.”

Image Credits: Photo by Myriam Zilles on Unsplash, Commons Wikimedia, WHO , WHO .