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NexGard and Simparica Trio are two of the most prescribed monthly chewables for dogs. Both belong to the isoxazoline class of parasiticides, both require a veterinarian’s prescription in the U.S., and both kill fleas and ticks. The key difference is scope: the original NexGard targets fleas and ticks only, while Simparica Trio combines flea and tick control with heartworm prevention and treatment of certain intestinal worms. This comparison summarizes what the labels say. It is not dosing advice; your vet decides which product and dose fits your dog.
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Active ingredients
NexGard (Boehringer Ingelheim) contains afoxolaner, an isoxazoline that kills fleas and ticks. Simparica Trio (Zoetis) contains three actives: sarolaner (an isoxazoline for fleas and ticks), moxidectin (a macrocyclic lactone for heartworm prevention) and pyrantel (for roundworms and hookworms). Note that Boehringer also sells NexGard PLUS (afoxolaner, moxidectin and pyrantel), which is Simparica Trio’s closer competitor; the original NexGard is a flea-and-tick product only.
NexGard® (afoxolaner) Flea and Tick Protection for Dogs Oral Soft Beef Flavored Chewables, 24.1 to 60 lbs. (Purple Box) 1 Chew (1 Month Supply)
Included for 'NexGard vs Simparica Trio Flea and Tick Comparison' because the listing specifies 24.1 to 60 lbs. (Purple Box) 1 Chew (1 Month Supply), details this guide uses to compare options.
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NexGard® (afoxolaner) Flea and Tick Protection for Dogs Oral Soft Beef Flavored Chewables,10.1 to 24 lbs. (Blue Box) 6 Chews (6 Month Supply)
Included for 'NexGard vs Simparica Trio Flea and Tick Comparison' because the listing specifies 10.1 to 24 lbs. (Blue Box) 6 Chews (6 Month Supply), details this guide uses to compare options.
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NexGard® (afoxolaner) Flea and Tick Protection for Dogs Oral Soft Beef Flavored Chewables, 60.1 to 121 lbs (Red Box) 1 Chew (1 Month Supply)
Included for 'NexGard vs Simparica Trio Flea and Tick Comparison' because the listing specifies 60.1 to 121 lbs (Red Box) 1 Chew (1 Month Supply), details this guide uses to compare options.
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NexGard® (afoxolaner) Flea and Tick Protection for Dogs Oral Soft Beef Flavored Chewables,10.1 to 24 lbs. (Blue Box) 1 Chew (1 Month Supply)
Included for 'NexGard vs Simparica Trio Flea and Tick Comparison' because the listing specifies 10.1 to 24 lbs. (Blue Box) 1 Chew (1 Month Supply), details this guide uses to compare options.
View on AmazonLabel comparison
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| Label feature | NexGard (afoxolaner) | Simparica Trio (sarolaner, moxidectin, pyrantel) |
|---|---|---|
| Prescription required | Yes | Yes |
| Dosing interval | Once monthly chewable | Once monthly chewable |
| Minimum age | 8 weeks | 8 weeks |
| Minimum weight | 4 lb | 2.8 lb |
| Fleas | Kills adult fleas; treats and prevents infestations | Kills adult fleas; treats and prevents infestations |
| Ticks | Multiple U.S. tick species listed on label | Multiple U.S. tick species listed on label |
| Lyme-related claim | Prevention of Borrelia burgdorferi infections by killing black-legged ticks (added 2018) | Same type of claim (added late 2021) |
| Heartworm prevention | No | Yes |
| Roundworms and hookworms | No | Treatment and control of listed species |
Always read the current package insert; indications are updated over time.
The FDA isoxazoline safety communication
In 2018 the FDA alerted owners and veterinarians that isoxazoline products, including afoxolaner and sarolaner, have been associated with neurologic adverse reactions such as muscle tremors, ataxia (loss of coordination) and seizures in some dogs, including dogs with no prior history. The labels were updated to include this information, and they advise caution in dogs with a history of seizures or neurologic disorders. The FDA has said these products remain safe and effective for most animals. If your dog has ever had a seizure, tell your vet before starting either product, and report any adverse reaction to your vet and the manufacturer.
Other label notes
- Simparica Trio contains a heartworm preventive, so dogs should be tested for existing heartworm infection before starting; it is not intended to treat adult heartworms.
- Safety in breeding, pregnant or lactating dogs has not been established for these products per their labels; discuss with your vet.
- Common side effects listed include vomiting, diarrhea, lethargy and reduced appetite.
- Neither product is labeled for cats.
How owners and vets decide
NexGard may fit when
- Your dog already takes a separate heartworm preventive you want to keep.
- You only need flea and tick coverage.
Simparica Trio may fit when
- You want one chew covering fleas, ticks, heartworm and common intestinal worms.
- You have a very small puppy close to the 2.8 lb minimum (with your vet’s guidance).
Regional parasite risk, your dog’s medical history and cost all factor in. Your vet will choose the right product and weight band.
Giving monthly chews correctly
Consistency matters more than the product. Give the chew on the same day each month, as the label directs, and record it on a calendar or app. Both labels note that the chews can be given with or without food; many dogs take them as a treat. Watch for a few minutes to make sure the whole chew is eaten, and check the label for instructions if a dog vomits shortly after dosing. Weigh your dog periodically, especially puppies, since the package is chosen by weight band and your vet may need to move your dog to the next size. Year-round protection is recommended in many regions because ticks and fleas can remain active in mild winters. Treat all dogs in the household, and ask your vet about appropriate products for cats, which must never receive dog-only products.
FAQ
Can I buy NexGard or Simparica Trio without a prescription?
No. In the U.S. both are restricted to use by or on the order of a licensed veterinarian. Legitimate pharmacies verify the prescription with your vet.
Are isoxazolines safe for my dog?
The FDA considers them safe and effective for most dogs, but they carry a neurologic warning. Discuss your dog’s history with your vet before use.
Bottom line
NexGard is a monthly flea-and-tick chew, while Simparica Trio adds heartworm prevention and intestinal worm control in one monthly chew. Both are prescription isoxazoline products with an FDA neurologic warning on the label. Follow the package directions exactly and let your veterinarian decide which fits your dog’s risks and history.
