Veterinarians Prioritize Convenience When Prescribing Cat Parasiticides

Veterinarians prescribing parasiticides for domestic cats continue to prioritize factors such as ease of administration and owner preference, relegating environmental concerns and resistance risks. Recent studies show that the persistence of these substances in the environment can affect insects and birds, raising questions for the One Health approach and the sustainability of veterinary practice.

A study by Hobbs and Duszak-Kowal involving 16 veterinarians in the United Kingdom found that 81% of professionals consider ease of administration the main criterion when choosing a parasiticide for cats. Owner preference also has significant influence, being decisive for 44% of respondents. In contrast, only 6% said that concerns about environmental contamination or drug resistance guide their prescription decisions. Prophylactic use was identified as the most effective strategy by 63% of participants, while only 38% keep up to date with parasiticide treatment guidelines.

Parasiticides from the isoxazoline class, such as fluralaner and lotilaner, are widely used in cats and dogs for flea and tick control. According to Berny and colleagues, these compounds have a fecal elimination half-life of 15.5 days for fluralaner and 22 days for lotilaner in cats, and can be detected in feces even after the recommended treatment period ends. The main route of elimination is biliary/fecal, which favors the release of these substances into domestic and natural environments. Simulations indicate that insects feeding on feces may be highly exposed to these active ingredients, especially fluralaner and lotilaner.

The environmental impact of veterinary parasiticides goes beyond invertebrates. A study published by Tassin-de-Montaigu and collaborators showed that residues of parasiticides applied to dogs and cats can contaminate bird nests when birds use animal hair to line their nests. A correlation was observed between the concentration of pesticides in hair found in nests and in unhatched eggs or dead chicks, suggesting direct transfer of substances to bird tissues. This reinforces the need to assess the environmental risks of veterinary products not only for insects but also for wild vertebrates.

Despite the concerning findings, the studies have important limitations. The research on parasiticide prescription was conducted with a small sample of 16 veterinarians and limited to certain regions of the United Kingdom, which may restrict the generalizability of the results. The studies on environmental persistence, while demonstrating the prolonged presence of compounds in the environment, still lack quantitative data on the real impact on insect and bird populations. Markowska-Buńka and colleagues highlight that, despite the efficacy and safety of isoxazolines for domestic animals, toxicity to non-target invertebrates and environmental persistence are emerging concerns that require integrated assessment.

The data suggest that environmental sustainability is still not a determining factor in the choice of parasiticides for cats, even in the face of evidence of environmental contamination and One Health risks. Most veterinarians prioritize convenience and owner preferences, while aspects such as resistance potential and ecological impact remain secondary. Experts advocate for stewardship programs and continuous professional development, as well as the creation of guidelines that incorporate environmental risk assessments into veterinary drug prescriptions.

In conclusion, although modern parasiticides are effective and safe for cats, their persistence in the environment and potential impact on non-target wildlife highlight the urgency for veterinary practices more aligned with One Health. Raising awareness and integrating environmental criteria into prescription decisions can contribute to a more sustainable and responsible approach to parasite control in companion animals.