FDA Alert: Neurological Risks in Flea and Tick Meds
FDA warns of seizures, tremors in dogs from isoxazoline flea/tick products like Bravecto, NexGard—know the risks and safe alternatives.
The U.S. Food and Drug Administration (FDA) has issued an important alert for pet owners and veterinarians regarding potential neurological adverse events associated with certain flea and tick prevention products for dogs and cats. These products belong to the isoxazoline class, which includes popular oral and topical treatments designed to protect pets from parasites. While these medications are effective for most animals, reports of serious side effects such as muscle tremors, ataxia (loss of coordination), and seizures have prompted the FDA to highlight these risks.
This alert stems from post-marketing surveillance data collected since the approvals of these drugs, revealing patterns of neurologic issues that were not as prominent during initial testing. Understanding these risks is crucial for making informed decisions about your pet’s parasite prevention, balancing the dangers of fleas and ticks against potential medication side effects.
What Are Isoxazolines?
Isoxazolines are a class of insecticides and acaricides (tick killers) that target the nervous systems of fleas and ticks, paralyzing and killing them upon biting the treated pet. Unlike older topical treatments that pets might ingest during grooming, isoxazolines are primarily administered orally in chewable tablets, making them palatable and convenient for pet owners. They provide long-lasting protection, often up to 12 weeks for some products against fleas and several types of ticks.
These drugs work by blocking certain neurotransmitter-gated chloride channels in invertebrate parasites, leading to hyperexcitation, paralysis, and death. However, this mechanism can sometimes affect mammalian nervous systems, particularly in sensitive dogs, resulting in adverse neurologic events. The FDA notes that while pre-approval studies showed safety for the majority, real-world use in diverse pet populations has uncovered rarer but serious reactions.
Affected Flea and Tick Products
The FDA specifically identifies several isoxazoline-containing products linked to neurologic adverse events. These include both oral tablets for dogs and some topical solutions for cats and dogs. Here’s a breakdown:
- Bravecto (fluralaner): Available as chewable tablets for dogs (protects against fleas and ticks for 12 weeks) and topical solution for cats and dogs.
- NexGard (afoxolaner): Chewable tablets for dogs, effective monthly against fleas and ticks.
- Simparica (sarolaner): Chewable tablets for dogs, monthly protection against fleas and multiple tick species.
- Credelio (lotilaner): Chewable tablets for dogs, targeting fleas and ticks monthly.
- Revolution Plus (selamectin and sarolaner): Topical solution for cats, combining flea, tick, heartworm, ear mite, and some intestinal parasite control.
These products received FDA approval after rigorous testing, but ongoing monitoring has led to label updates to warn about neurologic risks. For instance, Revolution Plus, approved later, already includes enhanced warnings, and manufacturers like Boehringer Ingelheim (for NexGard) have updated labeling accordingly.
Reported Neurological Adverse Events
The most commonly reported side effects from these isoxazoline products are neurologic in nature, affecting the central nervous system. Symptoms typically appear within hours to days after administration and can include:
- Muscle tremors: Uncontrolled shaking or twitching, often starting in the limbs or head.
- Ataxia: Loss of coordination, stumbling, or difficulty walking, resembling drunkenness.
- Seizures: Convulsions, which can range from mild to life-threatening cluster seizures.
Other associated symptoms may involve gastrointestinal issues such as vomiting, diarrhea, loss of appetite, and skin reactions. In severe cases, pets have experienced anxiety, hyperactivity, or even death. The FDA emphasizes that these events are seen consistently across the isoxazoline class, indicating a class effect rather than isolated to one product. Reports surged after widespread use, with data from the first few years post-approval showing higher incidences in dogs with pre-existing seizure histories or neurologic conditions.
Why Is the FDA Issuing This Alert?
The FDA’s alert, first issued on September 20, 2018, and updated in subsequent years (including 2019 and 2021), is based on adverse event reports from pet owners, veterinarians, and mandatory submissions from drug sponsors. Sponsors must report serious events within 15 days and provide periodic updates. Although these products are safe and effective for the majority of pets, the agency identified a signal for neurologic events warranting label changes.
Prior to approval, FDA scientists reviewed extensive data, but post-marketing reveals issues in larger, more varied populations. The alert aims to empower veterinarians and owners to assess individual risks, especially for dogs with seizure disorders, epilepsy, or breeds prone to neurologic issues. It’s not a recall—the products remain available—but a call for caution and informed choice.
History of the FDA Alert and Updates
The timeline of this issue began with the approval of Bravecto in 2014, followed by NexGard (2013), Simparica (2016), Credelio (2018), and Revolution Plus (2019). By 2018, enough reports accumulated for the initial alert. Updates expanded to new products and reinforced warnings. Independent studies, like Project Jake, corroborated higher rates of seizures and deaths than label expectations, though lower than some European data.
The FDA continues monitoring, paying extra attention in the first three post-approval years. This ongoing vigilance ensures pet safety amid flea and tick diseases, which can cause anemia, Lyme disease, and even death if untreated.
What Should Pet Owners Do?
- Consult your veterinarian: Discuss your dog’s health history, including any seizure-prone breeds (e.g., Collies, Australian Shepherds) or prior episodes. Vets can recommend alternatives.
- Monitor closely: Watch for symptoms 24-48 hours post-dose. Seek immediate vet care if tremors, ataxia, or seizures occur.
- Report adverse events: Use the FDA’s online portal or call 1-888-FDA-VETS to help track issues.
- Consider alternatives: Non-isoxazoline options include topical essentials like fipronil, natural repellents, or manual tick checks. Weigh flea/tick disease risks in your area.
Veterinarians should prescribe based on individual needs, not routinely. The FDA stresses these drugs’ benefits outweigh risks for most but urges personalized decisions.
Risk Factors and Vulnerable Dogs
Not all dogs react; risks increase with:
| Risk Factor | Description |
|---|---|
| Pre-existing seizures | Dogs with epilepsy or history of convulsions are at higher risk. |
| Breed predispositions | Herding breeds with MDR1 gene mutation (e.g., Collies) may metabolize drugs poorly. |
| Age/Size | Puppies, seniors, or small breeds may be more sensitive. |
| Overdose/Concurrent meds | Improper dosing or drug interactions amplify effects. |
Owners of at-risk dogs should explore safer preventives or environmental controls like yard treatments.
Alternatives to Isoxazoline Products
For safer flea and tick control:
- Topicals: Frontline (fipronil), Advantage (imidacloprid)—absorbed into skin, less systemic.
- Collars: Seresto (flumethrin/imidacloprid) for 8 months protection.
- Natural options: Essential oils (diluted cedarwood, lemongrass), diatomaceous earth, frequent bathing.
- Integrated pest management: Vacuuming, washing bedding, yard maintenance to reduce exposure.
Combine methods for best results, consulting vets for region-specific threats like Rocky Mountain spotted fever.
Frequently Asked Questions (FAQs)
Are isoxazoline products being recalled?
No, the FDA is not recalling them. They are considered safe for most pets but with highlighted risks.
Can my dog still use these meds if healthy?
Possibly, but discuss with your vet. Most dogs tolerate them well.
What if my dog has a reaction?
Stop use, contact your vet immediately, and report to FDA. Supportive care like anti-seizure meds may be needed.
Are there safer alternatives?
Yes, non-isoxazoline topicals, collars, and natural methods exist. Vet guidance is key.
How common are these side effects?
Rare, but consistent across the class. Exact rates vary, but reports are notable in post-marketing data.
Conclusion: Prioritizing Pet Safety
Flea and tick prevention is essential, but so is avoiding neurologic harm. Stay informed, work with your vet, and choose wisely. By heeding the FDA alert, you protect your dog’s health holistically.
References
- Animal Drug Safety Communication: FDA Alerts Pet Owners and Veterinarians About Potential Neurologic Adverse Events — U.S. Food and Drug Administration (FDA). 2018-09-20. https://www.fda.gov/animal-veterinary/cvm-updates/animal-drug-safety-communication-fda-alerts-pet-owners-and-veterinarians-about-potential-neurologic
- Fact Sheet for Pet Owners and Veterinarians about Potential Adverse Events Associated with Isoxazoline Flea and Tick Products — U.S. Food and Drug Administration (FDA). Accessed 2026. https://www.fda.gov/animal-veterinary/animal-health-literacy/fact-sheet-pet-owners-and-veterinarians-about-potential-adverse-events-associated-isoxazoline-flea
- New FDA Warning About Flea And Tick Medications — Dogs Naturally Magazine. 2018 (updated). https://www.dogsnaturallymagazine.com/new-fda-warning-about-flea-and-tick-medications/
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