Antimicrobial Stewardship Terms and Definitions


Antibiotic—a chemical substance produced by a microorganism that has the capacity, in dilute solutions, to inhibit the growth of or to kill other microorganisms. Often used interchangeably with “antimicrobial agent.”4

Antimicrobial—an agent that kills microorganisms or suppresses their multiplication or growth. This includes antibiotics and synthetic agents. Often used interchangeably with “antibiotic.”4

Antimicrobial resistance—a property of microorganisms that confers the capacity to inactivate or elude antimicrobials or a mechanism that blocks the inhibitory or killing effects of antimicrobials.4

Extralabel—actual use or intended use of a drug in a manner that is not in accordance with the approved labeling. This includes, but is not limited to, use in species not listed in the labeling, use for indications (disease or other conditions) not listed in the labeling, use at dosage levels, frequencies, or routes of administration other than those stated in the labeling, and deviation from the labeled withdrawal time based on these different uses.

Intrinsic resistance—inherent or innate (not acquired) antimicrobial resistance, which is reflected in all or almost all representatives of a bacterial species.19

Minimal inhibitory concentration (MIC)—the lowest concentration of an antimicrobial agent that prevents visible growth of a microorganism in an agar or broth dilution susceptibility test.19

Monitoring—includes periodic health surveillance of the population or individual animal examination. Therapeutic—treatment, control, and prevention of bacterial disease.4

Antimicrobial prevention of disease (synonym: prophylaxis):

  1. Prevention is the administration of an antimicrobial to an individual animal to mitigate the risk of acquiring disease or infection that is anticipated based on history, clinical judgment, or epidemiological knowledge.
  2. On a population basis, prevention is the administration of an antimicrobial to a group of animals, none of which have evidence of disease or infection, when transmission of existing undiagnosed infections, or the introduction of pathogens, is anticipated based on history, clinical judgment, or epidemiological knowledge.

Antimicrobial control of disease (synonym: metaphylaxis):

  1. Control is the administration of an antimicrobial to an individual animal with a subclinical infection to reduce the risk of the infection becoming clinically apparent, spreading to other tissues or organs, or being transmitted to other individuals.
  2. On a population basis, control is the use of antimicrobials to reduce the incidence of infectious disease in a group of animals that already has some individuals with evidence of infectious disease or evidence of infection.

Antimicrobial treatment of disease:

  1. Treatment is the administration of an antimicrobial as a remedy for an individual animal with evidence of infectious disease.
  2. On a population basis, treatment is the administration of an antimicrobial to those animals within the group with evidence of infectious disease.

Antimicrobial time-out—an active reassessment of an antimicrobial prescription 48–72 hours after first administration to allow medical staff to take into account laboratory culture and susceptibility testing results and the patient’s response to therapy and current condition.8

Watchful waiting—an approach to patient care in which the veterinarian believes a patient’s illness will likely resolve on its own but remains vigilant in case an antibiotic is later needed. The pet owner is provided with instructions on when and why to follow up with the veterinarian and given recommendations for nonantibiotic approaches to improve the patient’s comfort.8

Veterinarian/Client/Patient Relationship (VCPR)—a VCPR exists when all of the following conditions have been met:

  1. The veterinarian has assumed the responsibility for making clinical judgments regarding the health of the animal(s) and the need for medical treatment, and the client has agreed to follow the veterinarian’s instructions.
  2. The veterinarian has sufficient knowledge of the animal(s) to initiate at least a general or preliminary diagnosis of the medical condition of the animal(s). This means that the veterinarian has recently seen and is personally acquainted with the keeping and care of the animal( s) by virtue of an examination of the animal(s) or by medically appropriate and timely visits to the premises where the animal(s) are kept.
  3. The veterinarian is readily available for follow-up evaluation, or has arranged for emergency coverage, in the event of adverse reactions or failure of the treatment regimen.

*IDEXX Laboratories, Inc. and Zoetis generously supported the development of the 2022 AAFP/AAHA Antimicrobial Stewardship Guidelines and resources through an educational grant to AAHA.