WHO List of Medically Important Antimicrobials

By Dr. Linda Jacobson, Toronto Humane Society/CASCMA

The primary purpose of this blog is to draw readers’ attention to two documents that every veterinarian and technician should be aware of. (Yes, technicians too. Just as you have a responsibility to challenge your veterinarians on inadequate analgesia, you should challenge them on antimicrobial stewardship. Future generations of people and animals will thank you.)

The documents:

• One, Dr. Scott Weese’s new blog on the subject, “New WHO Medically Important Antimicrobial List” [link https://www.wormsandgermsblog.com/2024/02/articles/miscellaneous/new-who-medically-important-antimicrobial-list/ ]. As always. Dr. Weese provides a succinct summary explaining important concepts and decisions.
• Two, the WHO document itself – “WHO List of Medically Important Antimicrobials: A risk management tool for mitigating antimicrobial resistance due to non-human use”  https://cdn.who.int/media/docs/default-source/gcp/who-mia-list-2024-lv.pdf?sfvrsn=3320dd3d_2#page=13&zoom=100,0,0 

We use a lot of antimicrobials in shelter and community medicine practice. That’s because we see a lot of infectious disease, and also see a lot of animals who are sick but where we lack the opportunity or resources to make a definitive diagnosis – so antimicrobials are often used as a “do something” measure or as a therapeutic trial.  This is problematic. 

There should never be a circumstance where a veterinarian does not think carefully about whether and how to use antimicrobials, and whether alternatives (such as topical treatments, lavage, etc) are possible. BSAVA have some really good guidelines in their “Guide to Responsible Use of Antibacterials: PROTECT ME” [link https://www.bsavalibrary.com/content/book/10.22233/9781910443644#chapters ]

I’ll go out on what I think is a pretty short limb and say that most conditions we treat with antimicrobials are probably:

• Not bacterial infections;
• Bacterial infections that are self-limiting and don’t require antimicrobials;
• Bacterial infections that are not susceptible to the product we have available, or where the product may not adequately penetrate that space or organ;
• Susceptible to the antimicrobial we choose but could be resolved by narrower-spectrum products, shorter courses or alternative approaches.

In terms of the WHO document, I jumped right to the lists from page 19 (numbered 12) and beyond, as a lot of the initial clarification was provided by Dr. Weese. Some things that caught my eye were:

• Everything is important, highly important, priority or protected! There is no “dispensable” antimicrobial. They all need to be used with care and respect, and an eye to the future.
• Cefovecin (Convenia), which is often used in veterinary medicine, is in the second-highest category of importance, “Highest priority critically important”. This drug should be used sparingly, and not be a go-to just because of its ease of use.
• All of the quinolones fall into the same category as the 3^rd and 4^th generation cephalosporins like cefovecin. Use sparingly and only when truly indicated. 
• Anecdotally, a lot of shelters jump to azithromycin for upper respiratory infections – this falls in the third group, “Critically important”. Many less critical alternatives are available. It should not be a first-line empirical choice.
• Note that tylosin is also “Critically important”. There is compelling evidence that acute diarrhea in an otherwise healthy animal is frequently self-limiing and does not require any antimicrobials. In these patients, tincture of time or a probiotic/stool binder should be sufficient.
• Many of our staples, such as cefazolin, most of the penicillins, metronidazole, clindamycin and doxycycline are “Highly important”. This group contains most of the antimicrobials we use all the time, and it’s our responsibility to ensure that they remain effective and available to our patients in the future, by not over-using them.