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Simparica Trio is a prescription monthly chew for dogs that combines flea, tick, heartworm, roundworm, and hookworm protection in one dose. It is approved for dogs and puppies at least 8 weeks old and weighing 2.8 pounds or more.
Most reported reactions are digestive or short-lived, but sarolaner—the flea and tick ingredient—is an isoxazoline associated with tremors, loss of coordination, and seizures in some dogs. The risk deserves particular attention in dogs with a seizure history or another neurologic disorder.
What is Simparica Trio?
Simparica Trio is an oral, flavored, prescription-only medication for dogs. Each tablet contains three active ingredients:
| Ingredient | What it does |
|---|---|
| Sarolaner | Kills fleas and controls several species of ticks. |
| Moxidectin | Prevents heartworm disease caused by Dirofilaria immitis. |
| Pyrantel pamoate | Treats and controls certain roundworms and hookworms. |
It is labeled for oral use in dogs only. It can be given with or without food and is administered once a month.
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- Fast Acting Long-Lasting Dog Flea & Tick Control: One application of PetArmor Plus lasts up to 30 days providing nose to tail protection. A 6-dose package lasts six months
- Easy-to-use, Long-Lasting: PetArmor Plus tick and flea prevention for dogs comes with six (6) waterproof topical applications that provide your pet flea protection and control for six (6) months
What parasites does Simparica Trio cover?
According to the current U.S. label, Simparica Trio is used to:
- Prevent heartworm disease.
- Kill adult fleas and treat and prevent flea infestations caused by Ctenocephalides felis.
- Prevent Dipylidium caninum tapeworm infection when that infection would result from infected fleas on the treated dog.
- Treat and control lone star, Gulf Coast, American dog, black-legged, brown dog, and Asian longhorned ticks.
- Prevent Borrelia burgdorferi infection as a direct result of killing infected black-legged ticks.
- Treat and control specified roundworms and hookworms, including Toxocara canis, Toxascaris leonina, Ancylostoma caninum, and Uncinaria stenocephala.
What it does not cover
Simparica Trio is not a general tapeworm treatment. Its tapeworm indication is limited to preventing Dipylidium caninum infection by killing infected fleas. It does not treat every existing tapeworm infection or prevent tapeworm infections that do not depend on fleas.
Likewise, tick protection does not mean protection against every tick-borne disease. The label specifically identifies prevention of Borrelia burgdorferi infection through killing infected Ixodes scapularis ticks.
Simparica Trio dosage for dogs
The tablet is selected according to the dog’s current body weight. Do not split tablets or choose a strength based on an old weight.
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|---|---|---|---|
| 2.8–5.5 lb | 3 mg | 0.06 mg | 12.5 mg |
| 5.6–11.0 lb | 6 mg | 0.12 mg | 25 mg |
| 11.1–22.0 lb | 12 mg | 0.24 mg | 50 mg |
| 22.1–44.0 lb | 24 mg | 0.48 mg | 100 mg |
| 44.1–88.0 lb | 48 mg | 0.96 mg | 200 mg |
| 88.1–132.0 lb | 72 mg | 1.44 mg | 300 mg |
Dogs over 132 pounds need an appropriate combination of tablets prescribed by a veterinarian. The dog should consume the complete dose.
If you miss a dose
Give the missed dose as soon as you remember, then return to the regular monthly schedule. Do not give extra tablets to compensate unless your veterinarian specifically tells you to do so.
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- Effective, Waterproof Flea Treatment for Dogs: PetArmor Plus is a waterproof flea and tick treatment for dogs that kills fleas, eggs, larvae, ticks, and chewing lice up to 30 days after application
- Trusted, Vet Quality* Formula: This large dog flea and tick treatment contains fipronil and (S)-methoprene, the same active ingredients as FRONTLINE Plus for Dogs; PetArmor Plus for Dogs has a powerful formula that starts to kill fleas in 24 hours
- Break the Flea Cycle: Unlike other dog flea and tick prevention that may temporarily suppress flea activity, PETARMOR Plus Dog Flea Treatment works by effectively breaking the flea life cycle! Kill flea eggs and larvae to prevent re-infestation
- Fast Acting Long-Lasting Dog Flea & Tick Control: One application of PetArmor Plus lasts up to 30 days providing nose to tail protection. A 3-dose package lasts three months
- Easy-to-use, Long-Lasting: PetArmor Plus tick and flea prevention for dogs comes with three (3) waterproof topical applications that provide your pet flea protection and control for three (3) months
For heartworm prevention, the label recommends year-round monthly treatment. If prevention is seasonal in your area, treatment should begin within one month of the first expected mosquito exposure and continue until at least one month after the last exposure. When changing from another monthly heartworm preventive, give Simparica Trio within one month of the previous product’s last dose.
Common Simparica Trio side effects
In a 330-day field safety study, 272 treated dogs received 11 monthly doses. The reported reactions were:
| Reported reaction | Dogs affected |
|---|---|
| Vomiting | 14.3% |
| Diarrhea | 13.2% |
| Lethargy | 8.5% |
| Reduced appetite or anorexia | 5.1% |
| Increased urination | 3.7% |
| Hyperactivity | 2.2% |
| Increased thirst | 2.2% |
These are study results, not a prediction of what will happen to an individual dog. A single episode of mild vomiting or diarrhea may resolve, but ongoing or severe signs need veterinary advice.
In other field studies, diarrhea was reported after treatment for fleas, while diarrhea and vomiting were reported in dogs treated for roundworms. These reactions can also have causes unrelated to the medication, including dietary changes, infection, parasites, or another drug.
Neurologic side effects and seizures
Sarolaner belongs to the isoxazoline class. The FDA says isoxazoline products are considered safe and effective for most dogs and cats, but they have been associated with neurologic reactions such as:
- Muscle tremors
- Ataxia, or loss of coordination
- Seizures
These reactions have been reported in dogs both with and without a previous seizure history. The Simparica Trio label advises caution in dogs with a history of seizures or neurologic disorders. A dog does not need to have epilepsy for a seizure to be reported after treatment.
Rank #3
- The #1 name in flea and tick protection
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- Fast-acting, long-lasting flea and tick treatment thats waterproof 24 hours after application
- Protects from fleas and ticks for a full month
- Kills adult fleas, flea eggs, flea larvae, ticks, and chewing lice
One dog in a controlled laboratory study had a seizure 16 days after receiving Simparica Trio. Post-approval reports have also included vomiting, diarrhea (with or without blood), seizures, lethargy, reduced appetite, muscle tremors, ataxia, nonspecific behavioral changes, and itching. These reports do not establish how often the events occur or prove that Simparica Trio caused them; an underlying illness, another medication, or another cause may be involved.
When is Simparica Trio unsafe or unsuitable?
The label lists no known contraindications, but that does not eliminate the seizure-related precaution or the need for veterinary assessment in dogs with neurologic disease.
Dogs with seizures or neurologic disease
Tell your veterinarian about any seizure, tremor, abnormal movement, or neurologic diagnosis before starting Simparica Trio. The veterinarian may decide that the benefits outweigh the risks, select another preventive, or recommend closer monitoring.
Pregnant, breeding, or lactating dogs
Safety has not been evaluated in breeding, pregnant, or lactating dogs. It should not be described as proven safe for these dogs. Ask your veterinarian for an alternative or a risk-benefit assessment.
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Puppies and small dogs
The minimum labeled age is 8 weeks and the minimum labeled weight is 2.8 pounds. A puppy that is too young or too small should not receive the product unless a veterinarian gives specific direction.
Dogs with heartworm infection
Dogs should be tested for existing heartworm infection before receiving Simparica Trio. The medication prevents the development of heartworm disease but does not kill adult heartworms. A dog with an established infection may require adulticide treatment under veterinary supervision.
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- K9 Advantix II Extra Large Dog 30-day treatment & prevention protects dogs over 55 lbs. from fleas, ticks, mosquitoes, biting flies and lice
- Kills fleas within 12 hours of application
- Vet-recommended formula kills & repels on contact so fleas don’t have to bite your dog to die
- Easy-to-apply topical treatment is fragrance-free and waterproof after 24 hours
- No prescription needed
The fact that the product was studied in heartworm-positive dogs does not mean owners should start or continue it without veterinary guidance when a dog may be infected.
Collies and ivermectin sensitivity
In a specific study, ivermectin-sensitive Collies received Simparica Trio at one, three, and five times the maximum labeled dose. At five times the maximum dose, some developed ataxia, muscle fasciculations, and dilated pupils; all recovered by the third day.
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Drug interactions
In three controlled field studies, Simparica Trio was used alongside vaccines, antimicrobials, anthelmintics, antiprotozoals, steroidal and nonsteroidal anti-inflammatory drugs, anesthetics, and analgesics without associated adverse reactions.
That finding does not guarantee that every drug combination is risk-free. Give the veterinarian a complete list of prescription medicines, supplements, parasite treatments, and recent products before the first dose.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to do if your dog reacts
- Write down the details. Note the dose, time given, your dog’s weight, symptoms, and any other medication or supplement.
- Call your veterinarian. Contact the clinic promptly for vomiting, diarrhea, marked lethargy, appetite loss, itching, unusual behavior, tremors, or incoordination.
- Seek emergency care for severe signs. A seizure, collapse, breathing difficulty, repeated vomiting, or bloody diarrhea warrants an emergency animal hospital.
- Do not give another dose. Ask the prescribing veterinarian whether to continue Simparica Trio or switch products.
Suspected adverse events can be reported to Zoetis at 1-888-963-8471 or to the FDA at 1-888-FDA-VETS. An adverse-event report is useful for safety monitoring, but it does not by itself prove that the product caused the event.
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- K9 Advantix II Large Dog 30-day treatment & prevention protects dogs 21-55 lbs. from fleas, ticks, mosquitoes, biting flies and lice
- Kills fleas within 12 hours of application
- Vet-recommended formula kills & repels on contact so fleas don’t have to bite your dog to die
- Easy-to-apply topical treatment is fragrance-free and waterproof after 24 hours
- No prescription needed
Storage and handling
Store Simparica Trio at or below 86°F (30°C). Keep it secured away from dogs, cats, children, and other animals to prevent accidental ingestion or overdose.
The FDA’s April 8, 2025, labeling update added the Dipylidium caninum prevention indication, listed the Asian longhorned tick among the covered ticks, and added post-approval adverse-event information. Check the current package labeling and follow your veterinarian’s instructions, particularly if information on an older package differs.
Sources
- Current Simparica Trio prescribing information, DailyMed
- FDA fact sheet on potential adverse events associated with isoxazoline flea and tick products
- FDA animal drug safety-related labeling changes
The Bottom Line
Simparica Trio offers convenient monthly coverage for several important canine parasites, but it is not a treatment for every parasite and it does not kill adult heartworms. Vomiting, diarrhea, lethargy, and appetite loss are the most commonly reported reactions. Tremors, ataxia, seizures, unusual behavior, or severe gastrointestinal signs require prompt veterinary attention. A veterinarian should review your dog’s weight, heartworm status, neurologic history, pregnancy or breeding status, and other medications before treatment.
FAQ
Can Simparica Trio cause seizures in dogs without epilepsy?
Yes. Seizures have been reported in dogs with and without a previous seizure history. Sarolaner is an isoxazoline, a class associated with seizures, tremors, and ataxia. Contact a veterinarian before using it in a dog with a neurologic disorder and seek urgent care if a seizure occurs.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsDoes Simparica Trio treat tapeworms?
Only in a limited sense. Its label covers prevention of Dipylidium caninum infection as a direct result of killing infected fleas. It is not a general treatment for an existing tapeworm infection or for tapeworms acquired independently of fleas.
Can puppies take Simparica Trio?
It is labeled for puppies at least 8 weeks old and weighing at least 2.8 pounds. The dose must match the puppy’s weight. Puppies below either limit should not receive it without specific veterinary direction.
What should I do if my dog vomits after Simparica Trio?
Call your veterinarian for advice, especially if vomiting is repeated, severe, accompanied by lethargy or other signs, or occurs in a dog with another illness. Do not automatically repeat the dose, because doing so could cause an overdose.
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