FDA Alert: Potential Neurological Problems with Certain Flea and Tick Medications

The U.S. Food and Drug Administration (FDA) has issued important alerts regarding certain flea and tick prevention products that may pose neurological risks to dogs and cats. These concerns center on medications in the

isoxazoline class

, which have been linked to adverse events such as muscle tremors, ataxia (loss of coordination), and seizures in some pets. While these products remain approved and effective for most animals, pet owners and veterinarians are urged to weigh the risks carefully, especially for pets with pre-existing conditions.

What Are Isoxazoline Flea and Tick Products?

Isoxazoline products are a class of oral and topical medications designed to kill fleas and ticks by targeting their nervous systems. These systemic insecticides work by blocking nerve signals in parasites, preventing infestations for up to one to three months depending on the product. Popular brands include Bravecto (fluralaner), NexGard (afoxalaner), Simparica (sarolaner), and Credelio (lotilaner) for dogs, as well as Bravecto topical for cats and Revolution Plus (selamectin and sarolaner) for cats, which also addresses heartworms and ear mites. The FDA approved these based on pre-market studies showing safety and efficacy, but post-approval surveillance revealed patterns of neurological issues.

These medications are highly effective against fleas, ticks, and sometimes other parasites, making them a go-to for veterinarians in high-risk areas. However, their mechanism—disrupting GABA receptors and glutamate-gated chloride channels—can occasionally affect mammalian nervous systems, leading to the reported side effects.

The FDA’s Official Alert: Key Details

In September 2018, the FDA’s Center for Veterinary Medicine released an Animal Drug Safety Communication highlighting potential neurologic adverse events associated with isoxazoline products. This was updated in subsequent years to include newly approved drugs like Credelio and Revolution Plus. The agency emphasized that while the majority of pets tolerate these drugs well, consistent reports across the class warranted label updates to inform users.

• Date of Initial Alert: September 20, 2018
• Affected Products: Bravecto, NexGard, Simparica, Credelio (dogs); Bravecto topical, Revolution Plus (cats)
• Reason: Post-marketing data showing tremors, ataxia, seizures
• Action Taken: Manufacturers updated labels; Revolution Plus included warnings from approval

The FDA monitors adverse events through voluntary reports from pet owners, mandatory sponsor submissions, and public data. Serious events must be reported within 15 days, with ongoing surveillance for the first few years post-approval.

Symptoms of Neurological Adverse Events

Pet owners should watch for these signs after administering isoxazoline products, as they can appear within hours to days:

Symptom	Description	Severity
Muscle Tremors	Uncontrolled shaking or twitching	Mild to Moderate
Ataxia	Stumbling, loss of balance, wobbling	Moderate
Seizures	Convulsions, collapse, paddling limbs	Severe
Vomiting/Diarrhea	Gastrointestinal upset	Mild
Loss of Appetite	Refusal to eat	Mild
Skin Issues	Irritation or lesions	Mild

These symptoms stem from the drugs’ persistence in the body (1-3 months), maintaining high concentrations that may impact neural signaling in sensitive pets.

Who Is at Higher Risk?

Not all pets experience issues, but certain factors increase vulnerability:

• Pets with a history of seizures or epilepsy
• Dogs or cats with pre-existing neurological disorders
• Breeds prone to tremors, like Chihuahuas or other small dogs
• Pets on multiple medications that affect the nervous system
• Very young, senior, or debilitated animals

Veterinarians are advised to review medical histories before prescribing. The FDA stresses individualized decisions, noting these events are not common but significant enough for awareness.

Manufacturer Responses and Label Changes

In response to FDA requests:

• Revolution Plus: Included class-wide neurologic warnings at approval
• NexGard: Updated by Boehringer Ingelheim (after acquiring from Merial) with class statement
• Other makers (Merck for Bravecto/Simparica, Elanco for Credelio) added similar language

These changes ensure pet owners see warnings like: “Isoxazoline products have been associated with neurologic adverse reactions, including muscle tremors, ataxia, and seizures in some dogs and cats.”

What Should Pet Owners Do?

If your pet shows symptoms:

1. Contact your veterinarian immediately—do not wait
2. Report the adverse event to FDA’s Center for Veterinary Medicine via their online portal
3. Discuss alternatives if your pet has risk factors

For prevention, consult your vet about non-isoxazoline options, especially in low-infestation areas. The FDA reaffirms these products’ overall safety but prioritizes informed choice.

Alternatives to Isoxazoline Flea and Tick Prevention

Safer options exist for flea/tick control without neurological risks:

• Topical Non-Systemic: Frontline (fipronil) kills on contact
• Collars: Seresto (imidacloprid/flumethrin) lasts 8 months
• Natural Remedies: Essential oils (cedar, lemongrass), diatomaceous earth—use cautiously
• Environmental Control: Vacuuming, washing bedding, yard treatments
• Other Orals: Spinosad (Comfortis) for fleas only, though monitor for issues

Integrate with regular baths and grooming for best results. Always vet-approved.

Frequently Asked Questions (FAQs)

Are isoxazoline products being recalled?

No, the FDA has not recalled them; they are considered safe for most pets with updated warnings.

Can I still use Bravecto/NexGard/Simparica?

Yes, if your vet deems it appropriate after reviewing your pet’s history. Risks are low but real.

How common are these side effects?

Rare; majority of pets have no issues, but reports are consistent across products.

What if my dog had a seizure after taking these meds?

Seek emergency vet care and report to FDA. Discontinue and switch preventives.

Are there breed-specific risks?

Pets with seizure history or small breeds may be more sensitive; consult vet.

Updated since 2018?

Yes, alerts expanded to new products in 2019/2021; monitoring continues.

Long-Term Monitoring and Research

The FDA’s post-market surveillance includes peer-reviewed studies and sponsor data. Independent analyses, like Project Jake, report higher seizure/death rates than labels suggest, underscoring caution. Pet owners play a key role by reporting incidents, helping refine safety profiles. As of 2026, no major changes, but ongoing vigilance is advised.

In conclusion, while isoxazoline meds protect against dangerous parasites (e.g., Lyme-carrying ticks), awareness of risks empowers better decisions. Prioritize vet consultations for tailored protection.