Flea, Tick, & Heartworm medications & Seizures

Flea, Tick, & Heartworm Medications & Seizures in Dogs: What to Know

The Remedy Neurology team often receives questions about flea, tick, and heartworm medications and seizures in dogs. There’s a lot of information online suggesting flea medication can cause seizures, and that’s partially true. A small number of dogs have seizures linked to these medications. However, it’s not as common as some websites would have you believe. Reports suggest it happens in 0.01% of dogs, which makes it very rare.

Why Do Some Dogs Have Seizures From These Medications & Others Don’t?

We don’t fully understand why this reaction happens. However, it’s possible that it’s due to a problem with a system in the body called the blood-brain barrier. The blood-brain barrier protects the brain from various substances, including certainmedications. Flea, tick, and heartworm medication shouldn’t be able to cross a dog’s blood-brain barrier, and therefore shouldn’t get into the brain to cause seizures.

The vast majority of dogs have a normal blood-brain barrier. When the blood-brain barrier is not normal, either genetically or due to disease, these medications may get into the brain and cause seizures. There’s a test for one of these abnormalities, MDR-1, and depending on your dog’s breed, your veterinary team may recommend this test.

How Can I Tell If My Dog’s Seizures Are From A Flea, Tick, or Heartworm Medication?

If your dog is sensitive to one of these medications, a seizure or other neurologic signs usually happen within a day of the very first application or dose. There are rare reports of delayed reactions. If you changed flea medication in the last three months and your dog developed a seizure condition soon afterward, that’s a good indication that they shouldn’t take that medication. As long as your dog doesn’t take it, they shouldn’t have further seizures.

If your dog has seizures at times other than around medication administration, it’s unlikely that the medications are related to the seizures. Similarly, if your dog has been on the same medication for years without problems in the past, it’s likely that it’s still safe to use.

Think of it like an allergy. If you’re allergic to peanuts, your body reacts poorly to them, and so you avoid eating them. However, if you aren’t allergic to peanuts, you’re able to eat them without any problems.

What If My Dog Has Epilepsy or Another Seizure Disorder?

As far as the Remedy Neurology team knows, a dog with epilepsy is no more likely than a dog without epilepsy to have this adverse drug reaction. If your dog has used a flea, tick, or heartworm medication safely for years and later develops a seizure condition, it’s unlikely that these drugs affect the seizures.

Most patients don’t have a change in their seizure frequency when starting or stopping these medications. However, if you’re nervous, it’s always reasonable to choose a medication that doesn’t contain isoxazolines.

Always follow the prescription label and the plan your pet’s veterinary team provides. Before starting, stopping, or switching flea, tick, or heartworm prevention, talk with your veterinary team.

Dog outdoors – flea medication safety information for pets with seizures

Flea, Tick, & Heartworm medications & Seizures FAQs

  • Reports suggest this happens in 0.01% of dogs, which makes it very rare.

  • If your dog is sensitive, seizures or other neurologic signs usually happen within a day of the very first application or dose. There are rare reports of delayed reactions.

  • If seizures happen at times other than around medication administration, the medication is unlikely to be related.

  • If your dog has been on the same medication for years without problems, that medication is likely still safe to use.

  • As far as Remedy’s Neurology team knows, a dog with epilepsy is no more likely than a dog without epilepsy to have this adverse drug reaction.

  • Consider choosing a medication that doesn’t contain isoxazolines. The isoxazoline class has been associated with neurologic adverse reactions, including seizures, in some dogs, even though most dogs use these products safely.

  • We ask that all pets be picked up by 5 pm the day of their visit. This gives our team time to review results and care instructions with you.

  • Some test results will be available the same day, and we’ll review them with you before you leave. Other results, such as lab work or imaging interpretations, may require input from off-site specialists and take additional time. Once all results are available, we’ll schedule a complimentary telemedicine follow-up to review everything in detail and discuss next steps.

  • Yes. We offer telemedicine consultations for follow-up appointments, reviewing test results, and ongoing care when appropriate. Telemedicine is a convenient way to stay connected with our team and ensure your pet receives continuous care without the stress of another trip.

    We also offer limited initial consultations via telemedicine for pets whose only symptom is seizures or for pets who have already been seen by another board-certified veterinary neurologist and are being referred for surgery.