Antibiotic use and stewardship in people, animals and the environment
Antibiotics are prescribed and used in people and in animals, and their residues also reach bacteria in the environment; stewardship aims to reduce that use. In people they are prescribed where they are not needed, as for influenza. In animals the questions are how much of the antibiotic supply goes to them, what reduces use in food-producing animals, and how far prescribing in companion-animal practice falls short of the guidance.
Antibiotic prescribing in people
Studies show that antibiotics are overprescribed for influenza.
Antibiotics in animal farming and the environment
Eighty per cent of medically important antibiotics are used in animal farming to promote growth and control infections, and they contribute to antibiotic resistance. Farmed fish are fed large amounts of antibiotics, which stay in the water. In one doctor's account, doctors and other medical professionals are advised to be very careful with antibiotics in their patients, rightly, but are very rarely told that most antibiotics are used in the animal industry.
Antibiotic residues that reach the environment interact with natural bacteria, resulting in genetic mutations, and the bacteria form resistance to antibiotics. Antibiotic resistance is a huge global health threat. Resistance arising this way is an example of an impact on the environment coming back as an impact on human health.
Reducing antimicrobial use in food-producing animals
Antimicrobial resistance is one of the world's most pressing public health issues, and the use of antimicrobials in animals contributes to it. In January 2017 the European Medicines Agency stated that reducing the use of antimicrobials in food-producing animals, replacing them where possible and rethinking the livestock production system is essential for the future of animal and public health. Experts from the European Food Safety Authority and the European Medicines Agency who reviewed the measures taken in the EU to reduce antimicrobial use in animals stress that there is no one-size-fits-all solution. Successful strategies follow an integrated, multifaceted approach that takes account of the local livestock production system and involves every relevant party, from governments to farmers.
The measures fall under reduction, replacement and rethinking. On reduction, setting national targets to reduce antimicrobial use has been an important driver of change, use should be cut to the minimum necessary to treat infectious disease, use to prevent disease should be phased out in favour of alternative measures other than in exceptional cases, and antimicrobials critically important for human medicine should be used in animals only as a last resort. On replacement, the alternatives shown to improve animal health and thereby reduce the need for antimicrobials include vaccines, probiotics, prebiotics, bacteriophages and organic acids. On rethinking, the livestock system needs farming practices that prevent disease entering and spreading on farms, and alternative farming systems that are viable with reduced antimicrobial use need to be considered. Education and awareness of resistance should be addressed to every level of society, particularly veterinarians and farmers.
The experts considered it reasonable to assume that reducing antimicrobial use in food-producing animals would result in a general decrease in antimicrobial resistance in the bacteria those animals carry and in the food products derived from them, but for lack of data they could not quantify the impact of single reduction measures or alternatives to antimicrobials on resistance levels.
Prescribing on New Zealand dairy farms
Antimicrobials are essential in treating, preventing and controlling diseases of food animals. In New Zealand, the Agricultural Compounds and Veterinary Medicines Act regulates the prescribing of antimicrobials, and prescribing a restricted veterinary medicine such as an antibiotic requires a bona fide veterinarian-client relationship, which means visiting the farm at least once a year, although most farmers have more frequent visits. Vets hold an annual consultation with their clients to decide the season's allowance of restricted veterinary medicines and to ensure farm staff understand drug classes and uses. In one New Zealand dairy vet's practice, the consultation discusses common conditions on the farm such as mastitis, metritis and lameness, and vet and farmer together determine treatment strategies and estimate the medication needed from the farm's history, which lets farmers keep a stock of medicines on the farm for immediate treatment of common conditions. When conducted comprehensively, the consultation educates farmers on the effective and responsible use of medicines. In the same vet's experience, farmers are receptive to such discussions because inappropriate treatments are often unsuccessful and expensive, provided the vet takes an open, collaborative approach. When that vet's farmers meet a situation the consultation did not cover, they mostly call to confirm an appropriate treatment strategy, which the vet notes may not happen in every client-vet relationship. Through education, those farmers adopt an evidence-based, informed approach in collaboration with their trusted adviser rather than indiscriminately reaching for antibiotics.
The New Zealand Veterinary Association's guidelines on the judicious use of antibiotics set out a traffic-light system for prescribing that is based on the WHO classification and classifies antimicrobials by their importance to human medicine in the face of antimicrobial resistance:
- Green, first line: procaine penicillin, penethamate hydriodide and tetracyclines. Recommended against known susceptible organisms; where efficacy is in doubt, an amber or red antimicrobial with known efficacy is used. Green status does not mean that use is risk-free or that it is unimportant to human medicine.
- Amber, second line: aminoglycosides, semi-synthetic penicillins, first- and second-generation cephalosporins, lincosamides and potentiated sulphonamides. Of increased clinical importance to human medicine because of their class or specialised features, and not to be used in veterinary patients where efficacy is in doubt.
- Red: third- and fourth-generation cephalosporins, fluoroquinolones and macrolides. Considered critically important and used in treating refractory conditions in human and veterinary medicine; their routine use is discouraged.
The same vet uses the traffic-light system during the annual consultation to advise treatment plans for the common conditions the farmer encounters. Red antibiotics are the only exception to the season's allowance: access to them must be reviewed every four months, which in the vet's experience discourages the use of these critically important antibiotics.
The Dairy Antibiogram contributes to ethical product stewardship by monitoring antibiotic effectiveness on common mastitis pathogens in bulk milk samples. It uses broth microdilution, a quantitative test, to define the minimum inhibitory concentration. Agar disc diffusion assays were previously used to determine antibiotic sensitivities, but they have significant limitations and need care in interpretation. The antibiogram can be used to build a database through which antimicrobial use patterns and their effects on resistance can be monitored and investigated. Epidemiological cut-off values distinguish the wild-type population from the non-wild-type and so detect the emergence of antimicrobial-resistant phenotypes. The same dairy vet has found the antibiogram an indispensable tool for evidence-based guidance on prescribing antibiotics.
Regulation and trends in farm antibiotic use
Antibiotics were used as growth promoters in livestock until, following public pressure, New Zealand banned the practice in 2002 and Europe in 2006. Outlawing it increased the need for therapeutic antibiotics despite improvements in husbandry, and those therapeutic antibiotics overlapped more with those used in human medicine. Antibiotics are a critical global resource, and antimicrobial resistance is recognised as one of the most severe public health threats. On 28 January 2022 the EU enforced new regulations on veterinary medicines (Regulation (EU) 2019/6) and medicated feed (Regulation (EU) 2019/4), aiming to reinforce responsible antibiotic use. In parallel, the New Zealand Veterinary Association set the goal that by 2030 New Zealand will not need antimicrobials to maintain animal health and wellness.
The treatment and prevention of mastitis account for approximately 85% of antimicrobial use on New Zealand farms. Blanket dry cow therapy, giving intramammary antimicrobials to the whole herd at the end of the milking season, revolutionised mastitis control by curing current infections and preventing new ones in the dry period. Teat sealants and selective dry cow therapy then dramatically reduced antibiotic use on farms without affecting the cow's health and welfare or milk quality.
As of early 2023, New Zealand ranked as the third-lowest consumer of antimicrobials globally, behind Norway and Iceland, perhaps because of the extensive nature of its production systems. New Zealand Food Safety reported a steady decline in antibiotic use, with sales of multi-species products falling 5% from 2018 to 2019. A focus on minimising dry cow therapies cut antibiotic use by almost 20% over 2017–2019. In the United Kingdom, the latest Veterinary Antibiotic Resistance and Sales Surveillance data in early 2023 showed sales of antibiotics for livestock at their lowest levels, down 55% since 2014, and sales of antibiotics critically important for treating human disease down 83% since 2014. Reports from the European Medicines Agency indicate that sales of antibiotics for animal use almost halved between 2011 and 2021. In one New Zealand dairy vet's view, dairy vets strive to lead the way with prudent antimicrobial use.
Companion-animal prescribing against stewardship guidance
A retrospective study compared the antibiotic prescribing of first-opinion veterinarians in the United Kingdom with contemporaneous UK antibiotic stewardship guidelines, using the clinical records of 917 cats and dogs referred to the internal medicine and oncology departments of two referral hospitals. Of those animals, 486 (53.0%) had been prescribed antibiotics for the condition they were eventually referred for. The first-opinion vet had undertaken bacterial culture to support the prescription in 8.8% of cases and cytology in 1.8%. After work-up at the referral centre, a bacterial aetiology was found or suspected in 17.9% of the cases that had received antibiotics. The stewardship guidelines had not been followed in 344 of the 486 (70.8%). The authors concluded that infrequent culture and cytology may contribute to overprescription in this population, and that the barriers to performing those tests in practice need to be removed, alongside education initiatives to improve compliance with stewardship guidelines and reduce prescription rates.
A review of the clinical records of 7,387 dogs treated for urinary tract infection at 723 clinics in Canada and the United States, most of them first-opinion clinics, compared antimicrobial prescribing for the infection in 2016 and 2018 with reference to contemporary prescribing guidelines. The median length of antibiotic treatment prescribed for sporadic bacterial cystitis fell from 14 days in 2016 to 10 days in 2018 (P = .0002), and compliance with the recommended first-line treatment selection increased over the same period. These results show awareness of antimicrobial stewardship becoming more widespread and translating into a change in prescribing behaviour. However, the study also found an overall prevalence of 39% for using a "highest priority critically important" antibiotic as first-line treatment for canine urinary tract infection, which indicates a need to keep raising veterinarians' awareness of the responsible use of antimicrobials.