At a Glance
- French researchers found isoxazoline antiparasitic drugs persist in pet feces for weeks
- Two compounds-fluralaner and lotilaner-remained detectable after treatment ended
- Simulations show dung-feeding insects face high exposure in parks and yards
- Why it matters: Your dog’s monthly flea pill could be silently harming essential bugs that recycle waste
Pet owners reach for isoxazoline pills and chews because they kill both fleas and ticks for up to a month with a single dose. A newer injection, Bravecto Quantum, promises a full year of protection. The convenience has made these drugs a go-to since the first approval in 2013, but scientists now warn the same compounds may be quietly accumulating in the environment.
Study Tracks Drugs From Pill to Poop
Researchers at the University of Toulouse recruited 20 dogs and cats owned by veterinary students. Each animal received one of four common isoxazolines-fluralaner, (es)afoxolaner, lotilaner, or sarolaner-exactly as prescribed for three months. The team then collected fecal samples at regular intervals and measured drug concentrations.
Key findings:
- Median half-lives ranged from 15 to 25 days, varying by drug and species
- Fluralaner and lotilaner remained traceable after the treatment window closed
- All four drugs passed through the animals in active form
Wildlife Faces Hidden Risk
Using these half-life data, the group modeled how much drug residue enters the soil when treated pets defecate in parks, gardens, or along sidewalks. Their simulations focused on dung beetles and other insects that break down feces-species crucial for nutrient cycling and soil health.
Results indicated high exposure risk for these insects, especially from fluralaner and lotilaner. Because the drugs stay active in feces, every deposit becomes a small toxic hotspot that can linger for weeks.
The European Medicines Agency has already flagged similar concerns, citing expanding pet populations and rising isoxazoline sales as reasons to re-evaluate environmental safety. The new data add weight to that call.
What Pet Owners Can Do
Authors stop short of advising owners to abandon the medications, noting that flea and tick control remains essential for animal welfare. Instead, they suggest simple disposal changes during treatment periods:
- Bag pet waste and place it in trash headed for incineration where available
- Avoid composting feces from treated animals
- Keep dogs out of natural areas for a few days after dosing if possible
“Our preliminary assessment suggests that pet ectoparasiticides may be detrimental to the environment and supports the conclusions from the EMA scientific opinion,” the authors wrote in the paper, published Wednesday in Environmental Toxicology and Chemistry.
They stress the results are not proof of ecological collapse, but rather a signal that larger field studies are urgently needed to map how much drug is reaching wild insects and what the population-level effects might be.
Drug Makers Face New Scrutiny
No regulatory agency has moved to restrict isoxazoline sales, yet the French findings could accelerate reviews. The EMA’s existing opinion already asks manufacturers to supply additional environmental fate data for these compounds. If outdoor residues keep climbing, leash laws or disposal ordinances could follow.
For now, the simplest lever sits with owners: flush or trash the poop, not the planet.
