Judicious use of antimicrobials

Judicious use of antimicrobials

Policy type: Policy
: 2e
: Current
Date ratified
: 4 May 2015


These guidelines are intended to act as an adjunct to clinical judgment. It may not be possible for every consideration to be observed in every case, but they should always form part of an automatic checklist when deciding on an antibiotic use regime.

  1. The use of antibiotics provides an effective method for the control and treatment of infectious diseases caused by bacteria and certain other micro-organisms. Their use in veterinary practice since the 1950s has assisted in ensuring the health of livestock and companion animals. Antibiotic use has also enabled the production of meat, egg and milk products which are unlikely to present disease problems for the consumer or those concerned with their production. Antibiotic use is also justifiable on animal welfare grounds.
  2. In treating animals with antimicrobials, veterinarians should aim to optimise therapeutic efficacy and minimise the potential for development of resistance to antimicrobials.
  3. It must be remembered at all times that widespread use of antibiotics is not a substitute for efficient management or good husbandry practice. Treatment of disease is not as effective or as economical as prevention.
  4. Use of antimicrobials by veterinarians could possibly contribute to antimicrobial resistant bacteria developing in animals, with subsequent transfer to humans. Particular care should be taken when prescribing antibiotics which could give rise to cross resistance with drugs used for serious infections in people. These include 3rd and 4th generation cephalosporins and fluoroquinolones. These drugs should be avoided unless there is a good reason to use them rather than another class of antibiotic.

Principles of antibiotic use

  1. There must be evidence of bacterial infection, or a risk of imminent infection, to justify antibiotic use.
  2. The appropriate selection of antibiotics in practice is a critical decision and should be based on:
    a. accurate diagnosis
    b. known or predictable sensitivities (sensitivity testing)
    c. known pharmacokinetics/tissue distribution to ensure the selected drug reaches the site of infection
    d. known status of immunocompetence
    e. likelihood of compliance with dosing instructions.
  3. Antibiotics need to be used with care to maintain their efficacy. If possible, look for alternative methods of disease control (vaccination or management changes) or adjuncts to antibiotics (drain abscesses etc.) to reduce antibiotic use.

Routine considerations

  1. Antibiotics should only be used when it is known or strongly suspected that susceptible bacteria are present and causing, or likely to cause, disease.
  2. Before antibiotics are used, every effort should be made to find the origin of the problem and to ascertain the most effective treatment. In many cases, this will involve taking samples for culture and sensitivity testing, or in some cases involving epidemiological studies.
  3. The efficacy of all treatments should be monitored and, if part of the treatment regime was undertaken by the animal owner, a check should be made to ensure that they have understood fully the instructions on dosage and duration of any antibiotic use. Quantities of antibiotics prescribed to the animal(s) owner should correctly reflect the needs of the animal, herd or flock, to avoid an over-supply.
  4. Should there be recurrence of disease following successful treatment of an outbreak it will need to be investigated thoroughly to ascertain why this has occurred and the most suitable therapy to be used in future.
  5. All antibiotics must be used and stored correctly. Sterile technique with multi-use vials should be observed.

Drug selection

  1. While therapy may need to be initiated before the results of diagnostic or sensitivity tests are known, it will need to be reassessed as test results become available. Empirical choices of antibiotic will need to be made:
    a. in the light of what has previously been effective in similar types of problems
    b. on any knowledge of previous antibiotic efficacy or sensitivity testing on the premises
    c. based on relevant controlled clinical trial data where available.
  2. Infectious disease should be treated with an antibiotic found, on appropriate testing, to be efficacious. It should also be based on the previous history of effective antibiotic use on the premises.
  3. In order to minimise the likelihood of broad antibiotic resistance developing, where an appropriate narrow spectrum drug is available it should be selected in preference to a broad spectrum drug, which will exert a greater selection pressure on commensal bacteria. Antibiotics considered of high importance in human medicine should be avoided unless there is good reason to use them (e.g. where other available drugs are not likely to be effective).

Dosage strategy

  1. Optimal therapeutic dosage strategies should be used and all efforts made to avoid giving sub therapeutic dosages, which can lead to a lack of efficacy (and, in some specific cases, such as fluoroquinolones and erythromycin, has been shown to induce resistance). Treatment should be for as short a time as possible but for as long as necessary for the desired clinical response. Dosage recommendations as laid down in the registered ACVM label should be followed.
  2. Careful calculation of dose is always important, but in particular if a discretionary use of a product is being considered. In such cases, caution needs to be exercised regarding meat, egg and milk withholding periods.

Disease control programmes

  1. Antibiotic usage should always be part of, and not a replacement for, an integrated disease control programme. Such a programme is likely to involve hygiene and disinfection procedures, biosecurity measures, management alterations, changes in stocking rates, vaccination, etc. This applies to companion animals as much as to farm animals.
  2. Continued antibiotic use in such control programmes should be regularly assessed for effectiveness and whether such use can be reduced or stopped.
  3. Written protocols should be agreed between the veterinarian and the client as to when veterinary involvement is required in on-going disease conditions. These protocols must be regularly and frequently reviewed and updated. The appropriate review period will depend on the circumstances, but should not be longer than twelve months.
  4. Written protocols should be agreed for treatment of all enzootic conditions on the farm or premises. These protocols must be regularly reviewed and updated. They should outline the farmer’s obligations concerning the use of antibiotics. They should cover:
    • Storage
    • Administration techniques
    • Recording information to ensure compliance e.g. animal identification, product name, dose administered, date of treatment
    • Withholding times for meat, egg and/or milk
    • The correct dosage and duration of medication
    • The correct indications for use
    • The correct procedures for ensuring adequate withholding times.
  5. Use of antibiotics for the prevention of disease can only be justified where it can be shown that a particular disease is present on the premises, or is likely to become so, and that strategic antibiotic use will prevent clinical outbreaks of that disease. This strategy should only be employed in the short term and should be incorporated into or superseded by a preventative disease control programme. Prophylactic therapy should not use antibiotics of high importance to human health.

Regulatory concerns

  1. All antibiotics used for treatment or prevention of disease in New Zealand require a prescription. This means that the animal must be under the care of a veterinarian, who must have either examined the animal or obtained enough information about it to make a rational choice of treatment.
  2. Some antibiotics, which could give rise to resistance to vital human antibiotics, have extra conditions of use applied by the ACVM Group. These conditions should be checked on the ACVM website www.nzfsa.govt.nz/acvm/ and complied with.
  3. Any use of antibiotics outside the registered ACVM label should be carefully justified and documented, and comply with the Code of Practice for the Discretionary Use of Human and Veterinary Medicines by Registered Veterinarians.
  4. Note must be made, and documented, of any possible adverse reactions which may be observed, or a decline in efficacy of a previously effective antibiotic. Adverse reactions should be reported to the ACVM Group and the drug company.
  5. Consideration must always be given to the health of the person administering the products. Any necessary warnings should be issued.

References and supporting documents

These guidelines are based on the BVA guidelines Responsible Use of Antimicrobials in Veterinary Practice 2009 (pdf 45.91 kB)  with additions from the RUMA guidelines and the ACVIM consensus statement (J Vet Intern Med 19, 617–629, 2005).

New Zealand Food Safety Authority Adverse events report: Veterinary medicines (pdf 103 kB)