ECOTOXICITY OF PARASITICIDES IN THE UK
TABLE 5 Summary of recommendations regarding ectoparasiticide use in horses.
1 . Judicious use of ectoparasiticides will help limit their ecotoxic effects and reduce the selective pressure for resistance
2 . Testing of animals and only treating affected animals (or their direct contacts), will help minimise unnecessary use of these drugs
3 . Following topical treatment (such as with fipronil, permethrin or cypermethrin), there is a risk of contamination of both the immediate environment and water courses a. Avoid washing horses after any topical application b. Any spills should be mopped up with disposable material rather than washed down the drain
c. Packaging should not be rinsed out and should be disposed of carefully
d. Disposable gloves should be worn during application, reducing contamination of waste water from handwashing
4 . The ecotoxic effects of injectable doramectin are likely to be similar to oral ivermectin, although persistence in faeces may be significantly prolonged—consideration should be given to this potentially longer period of excretion
5 . Of the synthetic pyrethroids, permethrin degrades at a faster rate than cypermethrin and may therefore have a lower ecotoxic effect
6 . Topical application of macrocyclic lactones (ivermectin and moxidectin) should be avoided if possible
of home treatments rises (Czarny- Działak et al., 2020 ; Menzir & Adeladlw, 2022 ). Careful consideration must therefore be given to ensure safe disposal of product packaging associated with unused, partially used or expired medicines. As outlined by Murphy ( 2022 ), it is vital that veterinary medicinal
products are disposed of in accordance with local requirements as listed in the Summary of Product Characteristics. In general, these local requirements usually include some form of specialist incin- eration at an appropriately permitted facility. However, different types of veterinary medical products may require different disposal techniques (Menzir & Adeladlw, 2022 ) and there is no ‘one size fits all’ approach that can be taken. Veterinary professionals play an im- portant role in instructing clients on responsible medicine disposal at the point of prescribing (Epruma, 2023 ) and may wish to offer clients the opportunity to return used, unused and out- of- date med- icines to the practice. The importance of this has recently been rec- ognised in relation to antibiotics and antibiotic resistance, and a UK national campaign (‘antibiotic amnesty’) has been initiated by RCVS Knowledge to encourage clients to return unused and out- of- date antibiotic medications that have been prescribed for animals. A sim- ilar concern applies to anthelmintics and topical antiparasitic drugs used in veterinary species, including horses. Secondary packaging uncontaminated with the medicinal product, such as the outer card- board box, can be recycled/disposed of in accordance with local au- thority waste disposal rules. A study of medication disposal by human patients after discharge
from a hospital in the UK showed that patient habits varied by for- mulation and medication origin (Metezai, 2023 ). ‘Pharmacy return’ was the first choice for all formulations except topicals, drops and
CONCLUSIONS
In conclusion, despite the sparsity of direct evidence about the environmental impacts of equine anthelmintics and parasiticides, there is overwhelming evidence from other species that these same drugs can cause profound ecological damage. More judicious use of these drugs is required, not only to reduce environmental harm but also to reduce the pressure on the development of drug resistance. This will require a much greater focus on targeted and diagnostic- led
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patches, which primarily went into household waste. Post- survey patient conversations highlighted views that these drugs were ‘less harmful’. Conversations also highlighted that disposal was influenced by pharmacotherapeutic groups, for example, antibiotics would be returned to the pharmacy more commonly than simple analgesics, possibly due to dedicated national antimicrobial stewardship cam- paigns. Liquids had the highest response to being flushed down the toilet, suggesting patients underestimate their pharmaceutical value. ‘Pharmacy’ was the primary disposal route for all medications except those bought from nonpharmacy locations; these were pre- dominantly placed in household rubbish.
treatments and more emphasis on management practices
that control endo- and ectoparasites without the need for drug treatment. This, in turn, will require a significant change in deep- rooted behaviours and beliefs among both veterinarians and horse owners. With the current growing concerns about climate change and biodiversity damage, this has become a major issue that requires urgent attention.
AUTHOR CONTRIBUTIONS Callum J. Haseler: Conceptualization; data curation; formal analy- sis;
investigation; methodology; project administration; formal analysis; writ-
ing – original draft; writing – review and editing. Julia L. Shrubb: Conceptualization; data curation;
investigation;
methodology; project administration; writing – original draft; writing – review and editing. Hannah G. D. Davies: Conceptualization; data curation; formal analysis; investigation; methodology; project admin- istration; writing – original draft; writing – review and editing. David I. Rendle: Conceptualization; data curation; formal analysis; investi- gation; methodology; project administration; writing – original draft; writing – review and editing. Polly C. Rathbone: Conceptualization; data curation; formal analysis; investigation; methodology; project administration; writing – original draft; writing – review and editing. Timothy S. Mair: Conceptualization; data curation; formal analysis; investigation; methodology; project administration; writing – origi- nal draft; writing – review and editing.
CONFLICT OF INTEREST STATEMENT No conflicts of interest have been declared.
FUNDING INFORMATION There are no funders to report for this review article.
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