Use of antimicrobial drugs in veterinary practice

Policy

1. Veterinarians must use antimicrobials judiciously, in order to provide optimal healthcare for their patients, reduce the development of antimicrobial resistance (AMR) and preserve these critical medicines for future use.
2. Veterinarians should stress to owners the importance of routine preventive healthcare, animal husbandry techniques and infection control procedures to reduce the risk of disease and therefore reduce the need for antimicrobial therapy.
3. Infection control procedures and high standards of hygiene should be implemented in veterinary practice.
4. Veterinarians should prescribe according to published, evidence-based therapeutic antimicrobial guidelines, where available.

Background

Antimicrobials are essential tools for veterinarians to ensure the maintenance of health and welfare in companion animals, livestock, wildlife and other animals.

The term ‘antimicrobial’ refers to all antibacterial, antiviral, antifungal and antiprotozoal drugs.

Veterinarians rely on antimicrobials to treat animals and prevent suffering. It is critical that they are able to access these essential medicines and that they are prescribed responsibly. The AVA recognises and supports Australia’s conservative approach to the regulatory approval of antimicrobials and supports their use according to approved label directions.

The development of resistance to antibacterial drugs by bacterial populations is a growing global health issue, and this risk is increased by inappropriate use patterns, such as continuous use at subtherapeutic levels, or inappropriate choice of drug for the condition under treatment. Prudent use guidelines developed for veterinarians are therefore critical.

For the purposes of the remainder of this policy, the term “antimicrobial” is being used synonymously with “antibacterial”.

Therapeutic use of antimicrobials

Antimicrobials should only be prescribed or administered when the veterinarian has confirmed that bacterial disease is present or can reasonably be suspected on the basis of the animal’s clinical signs. This assessment should be based on clinical history, physical examination and, where appropriate, laboratory tests. The AVA recognises that physical examination of every individual in a herd or flock is often not possible. In cases where antimicrobial treatment of a herd or flock is required, veterinarians should, wherever possible, target the treatment to the affected classes of stock only and for the minimum period of time necessary to achieve effective therapy.

Prophylactic use of antimicrobials

Antimicrobials may be used prophylactically in groups of animals where there is a high risk of bacterial infection, during chemotherapy, in severely immunocompromised patients, in appropriate surgical cases and in cases of penetrating wounds where decontamination or disinfection is not likely to be fully effective. When using prophylactic antimicrobials for a surgical procedure, the prophylaxis should be initiated at a time that will allow plasma concentrations to reach effective levels at the commencement of surgery, and be discontinued after 24 hours unless there are sound reasons to continue treatment. Antibiotic prophylaxis should not be used as a substitute for optimal sterile technique.

Antimicrobial use in food-producing animals

Antimicrobials should only be used in food-producing animals when their use will result in improved animal health and welfare. Veterinarians should avoid using antimicrobials considered highly important to human health by ASTAG in food-producing animals if at all possible. Ideally susceptibility testing should be performed to ensure that an antimicrobial with a high importance rating is the only option for effective therapy.

Research and development into production systems and management interventions that minimise the need for antimicrobials while maintaining animal health and welfare, is essential.¹

Antimicrobials that are used as feed or water additives to target gastrointestinal microorganisms should wherever possible be chosen on the basis that they are from a class of antimicrobial that is not used in humans and should be prescribed in accordance with recognised best practice use.

Antimicrobial resistance (AMR)

Antimicrobial use in animals may contribute to the development and spread of bacterial resistance. The increasing frequency of AMR is a global health issue and poses significant risks to both human and animal health and welfare.² The veterinary profession accepts the responsibility to work with human health professions to reduce the likelihood of AMR in order to preserve the efficacy of these critical drugs.

Antimicrobial resistance in animal pathogens can lead to therapy failures, with subsequent adverse effects on animal health, welfare and productivity, as well as adverse economic and social effects on their owners.² Antimicrobial resistance can also be transferred between bacteria of humans and animals via the food chain, by direct contact between them and through environmental exposure.

• Antimicrobial use in the food chain has been shown to contribute to increasing levels of resistance in food-borne bacteria (e.g. E. coli, Campylobacter jejuni, Salmonella spp. and enterococci). However, appropriate food handling and cooking minimises the risk of transfer of bacterial resistance from the direct consumption of animal products.³
• Direct contact with treated animals can facilitate the transfer of resistant bacteria.^2,4,5 Veterinarians, farm workers and owners of pet animals being treated with antimicrobials, and those who handle animal products such as carcases, meat and offal, need to pay particular attention to hygiene during and after handling treated animals or their products.
• Environmental exposure may also pose a risk, with the transfer of antimicrobial resistance possible through contact with soil, water, plants and manure containing populations of resistant bacteria. Direct and indirect contact with wildlife that may carry resistant bacteria may also pose a risk.^2,6–8

Infection prevention

In the clinical setting, all veterinary staff should practice good infection prevention control procedures. Veterinarians should stress to owners the importance of routine preventative animal health care (i.e. vaccination, dental care, parasite control, hygiene, animal husbandry and adequate nutrition and exercise) to reduce the risk of bacterial disease and therefore reduce the need for antimicrobial therapy.

Guidelines: principles of good antimicrobial stewardship

Veterinarians should practice good antimicrobial stewardship in order to optimise the therapeutic effects of antimicrobials, while eliminating unnecessary use and minimising the development of AMR.

The principles of good antimicrobial stewardship are as follows.^9–13,18

1. Antimicrobials should only be administered, dispensed or prescribed when the veterinarian has confirmed that bacterial disease is present, or can reasonably be suspected as the cause of the animal’s clinical signs.
2. Assessment should be made of the likely target organisms (especially for empirical prescribing).
3. Antimicrobial susceptibility testing should be used:
   1. wherever possible as a matter of best clinical practice
   2. when there is suspicion of a complicated or life-threatening infection
   3. if the patient does not respond to initial treatment
   4. if the patient has a recurring or refractory infection
   5. if the patient is immunocompromised
   6. when there is a need to monitor the outcome of treatment (such as during long treatment periods)
   7. if the patient is at risk of infection with multi-drug resistant bacteria.
4. Antimicrobials should not be used for treatment of self-limiting infections in immunocompetent animals.
5. The choice of antimicrobial should be based on consideration of the properties of the drug, the pathogen, the infection site, the patient, ASTAG classification,and food safety.
6. The antimicrobial with the narrowest spectrum possible should be used to minimise the disruption of normal microflora and limit selection for resistance in bacteria that are not the target of the therapy.
7. Antimicrobials should be used for as short a time as needed to successfully treat the patient.
8. Topical therapy should be preferred over systemic therapy for treatment of superficial skin infections. Antimicrobial usage is not indicated in many superficial skin infections.^14,15
9. Off-label use should be avoided when appropriate on-label options are available.
10. Use of antimicrobials of high importance¹⁶ that are not registered for veterinary use should be restricted to rare and severe, life-threatening conditions in individual animals. Infection must be confirmed by culture and the antimicrobial therapy must have a reasonable chance of eliminating the infection, and the antimicrobial of high importance should be the most suitable option based on susceptibility testing.
11. Antimicrobial therapy should never be used as a substitute for good infection control or optimal medical and surgical practices.
12. Perioperative prophylaxis should only be used when necessary. It is not indicated for routine, aseptic surgery of less than 90 minutes duration where no pre-existing inflammation or infection is present, where neither the gastrointestinal or respiratory systems have been invaded, and aseptic technique is maintained. If required, it should be administered prior to surgery.
    1. Situations when perioperative antimicrobial therapy is appropriate include:
       1. prolonged surgical procedures (> 90 minutes)
       2. use of an implant or in-dwelling device
       3. procedures where infection would be catastrophic (e.g. CNS surgery, orthopaedic surgery)
       4. when there is an obvious break in asepsis
       5. bowel surgery with a risk of leakage
       6. closed contaminated wounds.
    2. In these situations, and where surgery is categorised as clean or clean-contaminated, antimicrobial therapy should be discontinued within 24 hours.
13. Potential toxicities, inter-current disease (especially kidney or liver disease) and physiological states that could influence drug action should be considered (e.g. pregnant, neonatal and geriatric patients).
14. If concurrent administration of different antimicrobials is indicated, the antimicrobials should not have an antagonistic or inhibitory interaction.
15. Clients should be educated to ensure compliance and to encourage adoption of good preventive healthcare for their animals (e.g. routine health checks, vaccination, parasite control, exercise and good nutrition)
16. Prescription of antimicrobials for a flock or herd must only be provided by a veterinarian with a bona-fide relationship¹⁷ with the individual farm and farm owner.
17. A veterinarian prescribing either an in-feed or in-water antimicrobial must have adequate knowledge of the mixing procedures or delivery systems required to ensure homogeneity of distribution of the medication to the animal and provide written instructions on duration of treatment.

Off-label use of antimicrobial drugs

Registered antimicrobials go through stringent peer-reviewed assessment before approval. Antimicrobials should only be used off-label (for a different species or indication, at altered dose rate or treatment interval) when there is no alternative, no registered veterinary drug available and only when state legislation permits this use.

The veterinarian should exercise considerable caution about the risks associated with off-label use of antimicrobials in food-producing animals because of the need to provide advice on appropriate withholding periods. The veterinarian should provide the client with written advice about withholding periods and export slaughter intervals, as the veterinarian may be liable for any residue violations should they occur. Preferably, use of highly important¹⁶ off-label antimicrobials in individual members of food-producing animal species should be restricted to those individuals that are not destined to enter the food chain.

Use of highly important antimicrobials in companion animals must only occur when there is compelling evidence that there is no suitable veterinary-registered antimicrobial available to treat the patient. Under such circumstances, particular care must be taken to ensure that:

• the animal is monitored regularly until completely recovered
• there is full compliance with prescribing instructions
• as far as possible, the animal is kept isolated from other animals and in limited contact with people.
• those in contact with the treated animal are advised about appropriate hand hygiene.

Where possible, off-label use of antimicrobials should be restricted to the treatment of individual animals.

Responsibilities of the veterinarian

Veterinarians must document any adverse reactions that are observed including any decline in efficacy of a previously effective antimicrobial. These should be reported to the manufacturer or the Australian Pesticides and Veterinary Medicines Authority.

All antimicrobials must be labelled, used and stored correctly, and be in date. Full records must be kept in accordance with statutory requirements.

Consideration must always be given to the health of the person administering the products, to the extent that they could be affected by antimicrobial-resistant microorganisms. Any necessary warning should be issued to ensure they understand and take all necessary hygiene precautions. Consideration should also be given to the risks posed by inadvertent exposure of personnel to the drug directly (e.g. if they are allergic to the medication.)

Ultimately, responsibility and accountability are individual matters and education (of producers, owners and veterinarians) is the best way to address any shortcomings in veterinary antimicrobial use. The owner of the animals needs to be as accountable for appropriate antimicrobial use as the veterinarian who prescribes and administers the antimicrobials.

References

1. Toutain P-L, Ferran AA, Bousquet-Melou A et al. Veterinary medicine needs new green antimicrobial drugs. Front Microbiol 2016;7:1196.
2. Laxminarayan R., Duse A., Wattal C. et al. Antibiotic resistance: the need for global solutions. Lancet Infect Dis 2013;13:1057–1098.
3. Koluman A, Dikici A. Antimicrobial resistance of emerging foodborne pathogens: status quo and global trends. Crit Rev Microbiol 2013;39:57–69.
4. Guardabassi L., Schwarz S, Lloyd DH. Pet animals as reservoirs of antimicrobial-resistant bacteria. J Antimicrob Chemother 2004;54:321–332.
5. European Medicines Agency. Reflection paper on the risk of antimicrobial resistrance transfer from companion animals. EMA, London, 2015.
6. Heuer H, Schmitt H, Smalla K. Antibiotic resistance gene spread due to manure application on agricultural fields. Curr Opin Microbiol 2011;14:236–243.
7. Woolhouse M., Ward M., van Bunnik B et al. Antimicrobial resistance in humans, livestock and the wider environment. Phil Trans R Soc B 2014;370:7.
8. Carroll D., Wang J., Fanning S et al. Antimicrobial resistance in wildlife: implications for public health. Zoonoses Public Health 2015;62:534–542.
9. Joint Expert Advisory Committee on Antibiotic Resistance (JETACAR). The use of antibiotics in food-producing animals: antibiotic-resistant bacteria in animals and humans. Commonwealth Department of Health and Aged Care, and Commonwealth Department of Agriculture, Fisheries and Forestry, Australia, Canberra, 1999.
10. Weese JS, Giguere S, Guardabassi L et al. ACVIM Consensus Statement on Therapeutic Antimicrobial Use in Animals and Antimicrobial Resistance. J Vet Intern Med 2015;29:487–498.
11. British Veterinary Association. Responsible use of antimicrobials in veterinary practice. November 2015. https://www.bva.co.uk/news-campaigns-and-policy/policy/medicines/antimicrobials/. Accessed January 2017.
12. British Small Animal Veterinary Association. BSAVA guide to the use of veterinary medicines 2nd edn. March 2016. https://www.bsava.com/Resources/Veterinary-resources/Medicines-Guide. Accessed January 2017.
13. Guardabassi L, Prescott JF. Antimicrobial stewardship in small animal veterinary practice: from theory to practice. Vet Clin North Am Small Anim Pract 2015;45:361–376.
14. De Jaham C. Effects of an ethyl lactate shampoo in conjunction with a systemic antibiotic in the treatment of canine superficial bacterial pyoderma in an open-label, nonplacebo-controlled study. Vet Ther 2003;4:94–100.
15. Murayama N.,  Nagata M.,  Terada Y et al. Efficacy of a surgical scrub including 2% chlorhexidine acetate for canine superficial pyoderma. Vet Dermatol 2010;21:586–592.
16. Australian Veterinary Association. Veterinary use of antibiotics highly important to human health. AVA Fact Sheet, April 2017. Accessed December 2018.
17. Australian Veterinary Association. Recommended key principles for veterinary practice Acts in Australia. May 2017. Accessed December 2018.
18. Prescott, J. F. and P. Boerlin (2016). "Antimicrobial use in companion animals and Good Stewardship Practice." Veterinary Record 179(19): 486-488.
19. Australian Veterinary Association. Guidelines for prescribing, authorising and dispensing veterinary medicines (2005, amended 2013). Accessed December 2018.

Related AVA policies and documents

Policies

Responsible use of veterinary medicines on farms (2010)

Veterinary use of compounded pharmaceuticals (2010)

Guidelines

Guidelines for prescribing, authorising and dispensing veterinary medicines (2005, amended 2013)

Guidelines for veterinary personal biosecurity (2017)

Veterinary use of antibiotics highly important to human health. AVA Fact Sheet (2017)

Codes of Practice

Code for infection control (1999) and associated guidelines

Code of practice for prescription and use of products which contain antimicrobial agents (2008) (Appendix 15)

Code of Practice for the use of prescription animal remedies (Schedule 4 substances) in the poultry industry (2005)

Other resources

www.ava.com.au/amr

Substances not permitted for use on food-producing animals in Australia