A contemporary approach to rational antimicrobial prescribing: Part 1
"As much as needed and as little as possible"
That's how the saying goes anyway. The aim is to keep antimicrobial exposure to a minimum to reduce the chance of resistance developing, whilst using as much as necessary to actually treat the infection. What bothers me about this mantra is that it is incredibly vague and abstract for the general practitioner. To make this concept easier to understand, I propose a different approach.
Start slow
What I mean by 'start slow' is to make sure that you really are dealing with a bacterial infection and have ruled out other potential treatment options before starting antimicrobials, where possible. This does not mean withholding antimicrobials when they are necessary, but refining our prescribing to situations where we are more confident that they are appropriately indicated.
Many diseases will be self-limiting with appropriate source control and symptomatic treatment alone, after all, otherwise healthy animals do have a competent immune system. It's also important to consider whether topical antimicrobial therapy will suffice, without the need for systemic antimicrobials. Similarly, many diseases can wait for microbiological results to guide antimicrobial therapy (also known as delayed prescribing).
Stop fast
The concept of the antibiotic course is outdated. Once clinical resolution of an infection has been achieved, antimicrobial treatment should be stopped.
Knowing when to stop is hard in veterinary medicine, as we primarily function as an outpatient-based service and our patients can't tell us how they feel. In practice, we have to assume that a resolution of clinical signs means resolution of infection, so what we can do is use shorter courses with rechecks to consider if treatment requires continuing.
Biomarkers
Another option to determine when to stop antimicrobial therapy is to use biomarkers as a monitoring tool. There is growing interest in using biomarkers such as C-reactive protein and serum amyloid A in animals to determine when to stop antimicrobial treatment. Far more work has been done in humans with procalcitonin and others. However, they are a rather blunt tool and while they do provide useful information for the clinician's decision-making process, they do not replace a good clinical exam. Check out the bibliography for examples.
The exception to the rule
Sepsis. In general, critical illness warrants earlier consideration for antimicrobial therapy and that goes doubly for sepsis. It is well documented in humans that early antimicrobial therapy saves lives in cases of sepsis. So it would be appropriate for every practitioner to be able to identify what is and is not sepsis.
Thankfully, there have been recent movements to update the definition in veterinary medicine. While we wait for the formal definition, the steering committee has released a narrative review of how human and veterinary sepsis definitions have evolved over time (see bibliography).
If you suspect sepsis, a 'Start fast, stop fast' approach would be more appropriate. Start antimicrobials when sepsis is suspected and stop them quickly if you rule it out.
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Llewelyn M J, Fitzpatrick J M, Darwin E, SarahTonkin-Crine, Gorton C, Paul J et al. The antibiotic course has had its day. British Medical Journal, 2017; 358:j3418 doi:10.1136/bmj.j3418
Spellberg B. 17 - Principles of Anti-infective Therapy. John E. Bennett, Raphael Dolin, Martin J. Blaser. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases (Ninth Edition). W.B. Saunders. 2019.
Spellberg B, Rice LB. Duration of Antibiotic Therapy: Shorter Is Better. Annals of Internal Medicine, 2019;171(3):210-211. doi:10.7326/M19-1509
Biomarkers:
Chwala M, Hartmann F, Waller K 3rd, Dusick A, Viviano K. Change over time and agreement between clinical markers of disease resolution in dogs with aspiration-induced lung injury. Vet Rec. 2023;192(8):e2280. doi:10.1002/vetr.2280
Fernandes Rodrigues N, Giraud L, Bolen G, et al. Antimicrobial discontinuation in dogs with acute aspiration pneumonia based on clinical improvement and normalization of C-reactive protein concentration. J Vet Intern Med. 2022;36(3):1082-1088. doi:10.1111/jvim.16405
Goggs R, Robbins SN, LaLonde-Paul DM, Menard JM. Serial analysis of blood biomarker concentrations in dogs with pneumonia, septic peritonitis, and pyometra. J Vet Intern Med. 2022;36(2):549-564. doi:10.1111/jvim.16374
Hamade B, Huang DT. Procalcitonin: Where Are We Now?. Crit Care Clin. 2020;36(1):23-40. doi:10.1016/j.ccc.2019.08.003
Sepsis:
Cortellini S, DeClue AE, Giunti M, et al. Defining sepsis in small animals. J Vet Emerg Crit Care (San Antonio). 2024;34(2):97-109. doi:10.1111/vec.13359
Evans L, Rhodes A, Alhazzani W, et al. Surviving sepsis campaign: international guidelines for management of sepsis and septic shock 2021. Intensive Care Med. 2021;47(11):1181-1247. doi:10.1007/s00134-021-06506-y