A new study reveals that isoxazoline-based flea and tick medications for dogs and cats can expose dung-feeding insects to toxic residues in pet feces. Researchers in France found traces of these drugs persisting in animal waste even after treatment ends. The findings highlight potential risks to ecosystems from routine pet care.
Widely used isoxazoline drugs, introduced in 2013, provide oral protection against fleas and ticks for pets lasting a month or more. These antiparasitic medications are prescribed by veterinarians globally, but their active ingredients pass through the animals' bodies and are excreted in feces, urine, and even shed hair.
The European Medicines Agency has previously cautioned that such veterinary treatments could contaminate ecosystems, though data on environmental entry levels has been limited. The primary worry involves unintended effects on non-target species, particularly insects that feed on dung.
In a study published in Environmental Toxicology and Chemistry by Oxford University Press, French researchers examined 20 dogs and 20 cats owned by veterinary students over three months. The animals received isoxazoline treatments, and scientists collected fecal samples to assess drug residues. Analysis detected two of the four common active ingredients in the feces, even beyond the recommended treatment period.
Dung-feeding insects, including flies, dung beetles, and certain butterflies, are crucial for breaking down waste, recycling nutrients, improving soil quality, and managing pests. An environmental risk assessment from the study indicates these insects could face high exposure levels from routine pet treatments, potentially disrupting ecological processes and affecting environmental lifecycles.
The research, led by Philippe J Berny, Bernadette España, Julie Auré, and Julia Cado, underscores the need for further investigation into how pet medications influence wildlife. The journal reference is: Prolonged fecal elimination of isoxazoline antiparasitic drugs in dogs and cats: is there a risk for nontarget species? Environmental Toxicology and Chemistry, 2026; 45 (2): 490. DOI: 10.1093/etojnl/vgaf285.
