WHO issues 'important antimicrobials list for human medicine' to combat antimicrobial resistance

The list categorizes antimicrobial classes based on their importance for human medicine and according to the AMR risk and potential human health implications of their use in non-human sectors: critically important, highly important, and important to human medicine.

Antimicrobials authorized for use in humans only.

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

Antimicrobial resistance (AMR) occurs when pathogens like viruses, bacteria, 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.

The document states, "The responsible and prudent use of antimicrobials needs to be improved in all sectors - animal, human, plant/crop, and environment - to preserve their public health benefits."

The WHO stressed that antimicrobials that are medically important for human medicine must be preserved by reducing their use in the non-human sectors.

The WHO List of Medically Important Antimicrobials for Human Medicine (WHO MIA List) is a risk management tool that can be used to support decision-making to minimize the impact of antimicrobial use in non-human sectors on antimicrobial resistance in humans.

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

The category, WHO explains, "mainly contains newer antimicrobials that are very important in treating serious multidrug-resistant infections in humans." 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.

Amone antimicrobials authorized “for use in humans only” are aminomethylcycline, plazomicin, carbapenems with or without inhibitors, anti-pseudomonal penicillins with and without β-lactamase 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 guide authorities in the public health and animal health sectors, veterinarians, agricultural professionals, and prescribers of antimicrobials, as well as classify antimicrobial categories by importance to human use, WHO said.

Drugs authorized for use in both humans and animals

A second category of medically important antimicrobials is drugs "authorized for use in both humans and animals."

This is further categorized into “highest priority critically important antimicrobials (HPCIA),” “critically important antimicrobials (CIA),” “highly important antimicrobials,” and “important antimicrobials.”

Widespread use of leading antibiotics in animals has become a major driver of rising 'superbug' resistance to common drug treatments, or AMR. In 1019, AMR led to the deaths of approximately 5 million people globally.

These risks can be addressed, by rationalizing the use of antimicrobial needs more systematically in both animal and 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.)

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

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

One health approach

The non-human use of antimicrobials includes a broad range of species beyond the historical focus on food-producing animals. These comprised companion animals, aquaculture, and fur-bearing animals. Reducing the use of antimicrobials in the non-human sector is important for preserving their efficacy, WHO said.

“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.

It is thus essential to decrease their inappropriate use across sectors to improve the prudent and responsible use of antimicrobial agents and, in particular, medically important antimicrobials.

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

Antimicrobial category ‘for use in animals only’

The WHO now includes an “authorized for use in animals only," in addition to the existing “highly important antimicrobials” (HIA) and “important antimicrobials” (IA) classifications.

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.”