Seizures from Simparica Trio are considered a rare but recognized adverse effect, falling under the category of neurological signs, which can occur in dogs without prior history, though the overall reporting rate for any sign is very low (less than 1 in 10,000 doses). While most dogs tolerate it well, the FDA and manufacturer Zoetis acknowledge potential neurological issues like tremors and seizures, and one study noted seizures in some animals, emphasizing that it's a known risk, especially with isoxazoline products.
Adverse reactions in dogs treated with SIMPARICA TRIO included diarrhea and vomiting. In one well-controlled laboratory study, one dog had a seizure 16 days after administration of SIMPARICA TRIO.
For pets with a history of seizures living in tick areas
These pets may have a greater risk of side effects. Your vet can discuss alternative products, such as Advantix (for dogs only) or a Seresto collar (for dogs and cats).
Simparica Trio is a broad-spectrum parasite control medication. Reported adverse effects like seizures or neurological issues are rare. Symptoms to watch include tremors, lethargy, or unusual behavior. Most dogs tolerate it well, but always monitor after administration. Consult your vet if side effects occur.
The best prescription alternatives to Simparica Trio include NexGard PLUS, Interceptor Plus with Bravecto or NexGard, and Credelio Quattro. These are made by trusted veterinary pharmaceutical companies like Boehringer Ingelheim, Elanco, Zoetis, and Virbac.
Simparica Trio™ has not been evaluated in dogs that are pregnant, breeding or lactating. Simparica Trio™ has been safely used in dogs treated with commonly prescribed vaccines, parasiticides and other medications. Use with caution in dogs with a history of seizures.
Both products are safe for dogs when following directions and have been approved by the FDA to treat and prevent flea and tick infestations. While Simparica was trialed and not approved, Nexgard has not yet been evaluated for use in breeding, pregnant, or lactating dogs.
Isoxazoline drugs can cause neurologic (nerve and brain) side effects if given incorrectly or if an overdose occurs. These issues include muscle tremors, ataxia (difficulty walking), and seizures. Other serious side effects may include nonstop vomiting or complete loss of appetite.
One class of medications, called isoxazolines, has been associated with seizures and other neurologic symptoms in some cats and dogs. Products that include isoxazolines include Bravecto, Nexgard, and Simparica and Credelio. In one report, Simparica had the highest incidence of reports of seizures.
Toxicity in dogs can show up anywhere from minutes to several days or even months after exposure, depending entirely on the substance; some toxins (like alcohol or certain pesticides) are rapid, causing symptoms like drooling or seizures quickly, while others (like some rat poisons) cause delayed internal bleeding over days, requiring immediate veterinary attention even if the dog seems fine. Always contact your vet or the Pet Poison Helpline (855-764-7661) immediately if you suspect poisoning, even without symptoms.
Our Vet Pick: Best Flea Medicine for Dogs With a History of Seizures. Our team of veterinary professionals recommend Comfortis as a potentially safer flea prevention for many dogs who experience seizures.
Common human medications that are potential toxins that cause dog seizures:
Cedarwood oil solution (10 drops per 1 ounce of water) can be applied to both pets and the environment once to twice daily. Cedarwood mulch is a helpful deterrent for landscaping. For moderate infestations, Dr. Trish uses Revolution and for severe infestations, she recommends Nexgard.
It's not uncommon for pets to experience mild side effects after taking medication like Simparica Trio. Lethargy can occur, but it's crucial to watch for any severe reactions such as vomiting or seizures. If your dog's lethargy continues or they show signs of distress, contacting your vet is the best course of action.
Once your pet has tested negative for Heartworm, Advantage Multi is a wonderful option. Advantage Multi is a topical Heartworm preventative. This is distributed to your pet by parting the fur on the back of their neck and applying directly to their skin. This product is approved for dogs with seizures.
The most common signs of toxicity from pyrethrum-based flea products are muscle tremors and excessive salivation. Common signs of organophosphate-based flea product toxicity include diarrhea, vomiting, difficulty breathing, small pupils, muscle tremors, weakness or falling over, and drooling.
Idiopathic epilepsy, the most common cause of seizures in the dog, is an inherited disorder, but its exact cause is unknown.
If synthetic chemical products are necessary for additional flea or tick control, NRDC recommends s-methoprene or pyriproxyfen, which are less toxic ingredients—but read the labels carefully because some products use them with other, more harmful pesticides.
Side Effects of Simparica Trio for Dogs
Simparica, like other flea and tick medications, is generally well tolerated by pups. However, in clinical studies, the most common side effect was gastrointestinal discomfort. This could present as vomiting or diarrhea after administration.
Safe for Most Dogs: When used as directed by a veterinarian, Simparica Trio is generally safe and effective for most dogs. Possible Side Effects: Some uncommon side effects include vomiting, diarrhea, lethargy, loss of appetite, and skin irritation.
How long does Simparica protection last? Simparica is a monthly chewable that starts protecting in hours* and lasts for 35 days. That gives you a little wiggle room at the end of the month, in case you're late with the next month's dose.
Increased itching after Simparica Trio may indicate an allergic reaction or sensitivity. Symptoms include aggressive scratching, redness, and bleeding. Causes can be medication ingredients or secondary flea allergy dermatitis.
Veterinarians may recommend Simparica Trio, a monthly chewable tablet that prevents against heartworm, fleas, ticks, and intestinal parasites.
Because heartworms must be eliminated before they reach this adult stage, it is extremely important that heartworm preventives be administered strictly on schedule (monthly for oral and topical products and every 6 months or 12 months for the injectable).
When considering time to efficiency between these two, we'll consider it a tie. Both products are safe for dogs when following directions and have been approved by the FDA to treat and prevent flea and tick infestations.