Update (June 21, 2026): Isoxazoline Neurological Safety Signal Concentrated in Dogs With Impaired Drug Efflux

TL;DR

Two 2025-2026 reviews reinforce that isoxazoline ectoparasiticides have wide safety margins but carry a rare, sometimes serious neurological adverse-event signal, with risk concentrated in dogs with impaired drug efflux such as ABCB1/MDR1 variants.

What just dropped

• A 2026 pharmacology and toxicology review (Markowska-Bunka et al., Int J Parasitol Drugs Drug Resist, https://europepmc.org/article/MED/42013589) concludes that controlled studies generally demonstrate wide safety margins for fluralaner, afoxolaner, sarolaner and lotilaner, but that post-marketing pharmacovigilance has identified rare but sometimes serious neurological adverse events, particularly in predisposed animals or in the context of impaired efflux transport such as ABCB1/MDR1 mutations or P-glycoprotein inhibition.
• A 2025 systematic review of fluralaner across mammals (Jiang and Old, PeerJ, https://europepmc.org/article/MED/40093406) graded the drug as moderately safe; of the 19 studies that reported side effects, one included signs of severe neurological toxicity.
• Both reviews note that the long elimination half-lives of these lipophilic compounds raise additional questions about tissue accumulation and delayed effects.

Context

The neurological signal is mechanistically plausible: isoxazolines block arthropod GABA- and glutamate-gated chloride channels, and although their affinity is far higher for arthropod than mammalian receptors, reduced P-glycoprotein function can raise central exposure in susceptible dogs. The systematic review also cautions that much of the published safety data come from small studies of fair methodological quality, so absolute event rates remain uncertain even as the products perform well in controlled trials.

What this changes in Fluralaner (Bravecto) for Canine Generalized Demodicosis

For the demodicosis use case, where isoxazolines are given monthly to clinical cure, these reviews support taking a medication and breed history before treatment and reassessing promptly if neurological signs appear — without changing the favorable overall efficacy and tolerability picture.

References

1. Markowska-Bunka P, Rasinski B, Ziolkowski H. 2026. Pharmacology and toxicology of veterinary isoxazolines: a review. Int J Parasitol Drugs Drug Resist 31:100645. https://europepmc.org/article/MED/42013589 [via]
2. Jiang Y, Old JM. 2025. A systematic review of fluralaner as a treatment for ectoparasitic infections in mammalian species. PeerJ 13:e18882. https://europepmc.org/article/MED/40093406 [via]

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Related reads

• Fluralaner (Bravecto) for Canine Generalized Demodicosis: Field Study Evidence
• Sarolaner Canine Generalized Demodicosis