NexGard vs. Bravecto vs. Simparica Trio: Choosing the Right Flea & Tick Prevention

You’re at the vet’s office, staring at three different flea and tick prevention boxes, and the prices are all different, the coverage looks similar, and you have no idea which one to pick. Your vet might recommend one, but you want to understand why — and whether it’s actually the best choice for your dog.

Here’s the short version: NexGard, Bravecto, and Simparica Trio are all effective flea and tick preventions from the same drug class. The differences come down to dosing schedule, what additional parasites they cover, and cost. All three carry the same FDA safety warning.

This guide will break down the real differences so you can have an informed conversation with your vet.

This is educational content only. Always follow your vet’s specific instructions for your pet’s medication.

What All Three Have in Common

Before we compare them, it helps to understand what unites them:

• Drug class: All three are isoxazolines. They work by blocking a specific receptor in the flea and tick nervous system, causing paralysis and death. This mechanism is highly specific to parasites and doesn’t affect mammals the same way.
• Form: Flavored chewable tablets your dog eats like a treat.
• Prescription required: You can’t buy any of these over the counter. A veterinary exam and prescription are required.
• Kill mechanism: They work after the parasite bites your dog. The parasite ingests the drug through your dog’s blood and dies. They do not repel parasites — they kill them after attachment.
• FDA class warning: In 2018, the FDA issued a warning that isoxazoline products have been associated with neurological adverse events in some dogs (muscle tremors, ataxia, seizures). More on this below.

Head-to-Head Comparison

Here’s what sets them apart:

NexGard (afoxolaner)

Dosing: One chew every 30 days

What it kills:

• Fleas (starts killing within 4 hours, 100% within 24 hours)
• Black-legged ticks (deer ticks)
• American dog ticks
• Brown dog ticks
• Lone star ticks

What it doesn’t cover: Heartworm, intestinal parasites. You’ll need a separate heartworm preventive like Heartgard.

Age/weight requirement: Dogs 8 weeks and older, 4 pounds and up

Speed: Starts killing fleas within 4 hours — the fastest of the three.

Manufacturer: Boehringer Ingelheim

Bravecto (fluralaner)

Dosing: One chew every 12 weeks (3 months)

What it kills:

• Fleas (starts killing within 2 hours, though full efficacy takes longer)
• Black-legged ticks
• American dog ticks
• Brown dog ticks
• Lone star ticks (for 8 weeks, not the full 12)

What it doesn’t cover: Heartworm, intestinal parasites. You’ll still need a separate product.

Age/weight requirement: Dogs 6 months and older, 4.4 pounds and up

Speed: Starts killing fleas within 2 hours.

Key advantage: One chew lasts 12 weeks instead of 4. That’s 4-5 doses per year instead of 12.

Manufacturer: Merck Animal Health

Important note: Lone star tick protection only lasts 8 weeks, not the full 12-week dosing period. If lone star ticks are common in your area, discuss this gap with your vet.

Simparica Trio (sarolaner + moxidectin + pyrantel)

Dosing: One chew every 30 days

What it kills:

• Fleas (starts killing within 4 hours)
• Five tick species (black-legged, American dog, brown dog, lone star, Gulf Coast ticks)
• Heartworm (prevents)
• Roundworms
• Hookworms

What sets it apart: This is the only one of the three that includes heartworm and intestinal worm prevention. One chew replaces what would otherwise be two or three separate products.

Age/weight requirement: Dogs 8 weeks and older, 2.8 pounds and up

Speed: Starts killing fleas within 4 hours.

Manufacturer: Zoetis

The Comparison Chart

Feature	NexGard	Bravecto	Simparica Trio
Dosing	Monthly	Every 12 weeks	Monthly
Fleas	Yes	Yes	Yes
Tick species	4	4 (Lone star: 8 wks)	5
Heartworm	No	No	Yes
Intestinal worms	No	No	Yes
Minimum age	8 weeks	6 months	8 weeks
Minimum weight	4 lbs	4.4 lbs	2.8 lbs
Doses per year	12	4-5	12
Approximate cost/month	$15-22	$13-18	$20-30

Costs are approximate and vary by dog weight, location, and retailer. Ask your vet for current pricing.

The FDA Neurological Warning: What It Means for Your Dog

In September 2018, the FDA issued a class-wide alert for isoxazoline products, reporting that some animals experienced muscle tremors, ataxia (wobbliness), and seizures after taking these medications.

Here’s what you need to know:

How Common Are These Reactions?

Rare. The FDA’s adverse event reports represent a small fraction of the millions of doses given annually. Most dogs take these products for years without any neurological issues.

That said, “rare” doesn’t mean “impossible,” and the reactions can be serious when they do occur.

Which Dogs Are Most at Risk?

• Dogs with a history of seizures or epilepsy. The FDA specifically warns about use in dogs with neurological disorders.
• Dogs sensitive to the drug class. If your dog has reacted to one isoxazoline, they may react to others.
• MDR1 gene mutation carriers. Certain breeds (Collies, Australian Shepherds, Shetland Sheepdogs, and some others) carry a gene mutation that affects how they process certain drugs. While isoxazolines are not specifically MDR1-affected, discuss this with your vet if your dog is a carrier.

What to Watch For

After giving any isoxazoline product, monitor your dog for:

• Muscle tremors or twitching
• Wobbliness or loss of coordination
• Seizures
• Excessive drooling or vomiting

If you notice any of these, contact your vet immediately. Most reactions occur within 24-48 hours of dosing.

Should You Be Worried?

For most dogs, the benefits of parasite prevention far outweigh the small risk. Tick-borne diseases like Lyme disease, ehrlichiosis, and anaplasmosis can be debilitating or fatal. Flea infestations cause suffering and can transmit tapeworms. Heartworm is deadly.

The question isn’t whether to use parasite prevention — it’s which one is right for your specific dog.

How to Choose: A Decision Guide

Choose NexGard if:

• You want straightforward monthly flea and tick prevention
• You’re already happy with your current heartworm preventive and don’t want to change
• Your dog is under 6 months old (Bravecto requires 6 months minimum)
• Cost is a consideration and you prefer a lower per-dose price point

Choose Bravecto if:

• You want fewer doses per year (4-5 instead of 12)
• You have trouble remembering monthly medications
• Your dog tolerates the larger chew (Bravecto chews are bigger because they contain more active ingredient for the longer duration)
• Lone star ticks are not a major concern in your area

Choose Simparica Trio if:

• You want to simplify your dog’s parasite prevention into one monthly chew
• Your dog currently takes separate flea/tick and heartworm medications and you’d prefer one product
• You want the broadest coverage (5 tick species plus heartworm plus intestinal worms)
• You’re starting a puppy on prevention for the first time and want an all-in-one approach

The Heartworm Test Requirement

If you’re considering Simparica Trio or any heartworm preventive, your dog must be tested for heartworm first. Giving heartworm prevention to a dog that already has heartworm can cause serious, potentially fatal reactions.

Your vet will run a simple blood test. If negative, your dog can start prevention right away. This test is typically done annually.

Topical and Non-Isoxazoline Alternatives

If your dog can’t take isoxazolines (due to seizure history or prior reactions), there are alternatives:

• Frontline Plus (fipronil + methoprene): Topical applied monthly. Kills fleas and ticks. No neurological class warning. Less effective than isoxazolines in some studies.
• Seresto collar (imidacloprid + flumethrin): Worn continuously, provides 8 months of flea and tick prevention. No oral medication needed.
• Advantix (imidacloprid + permethrin): Topical for dogs only. Also repels mosquitoes. Toxic to cats — do not use in households with cats who might contact the dog before the product dries.
• Heartgard (ivermectin + pyrantel): Monthly chewable for heartworm and intestinal parasites. Commonly paired with NexGard or Bravecto for dogs not using Simparica Trio.

Discuss alternatives with your vet. They’ll factor in your dog’s health history, your region’s parasite risks, and your lifestyle.

Questions to Ask Your Vet

When discussing flea and tick prevention, bring these questions to your appointment:

1. Which parasites are most common in our area? Regional risk varies significantly. Gulf Coast tick prevention matters in the Southeast but less so in the Pacific Northwest.
2. Does my dog have any risk factors for the neurological side effects? Seizure history, breed-specific sensitivities, or concurrent medications.
3. Is the all-in-one approach (Simparica Trio) right for my dog? Or would separate products give better flexibility?
4. What’s the actual cost difference over 12 months? Factor in the separate heartworm prevention you’d need with NexGard or Bravecto.
5. Is year-round prevention necessary where we live? In some climates, parasite activity drops in winter. Your vet knows local patterns.

When to Call Your Vet

Contact your vet if, after giving any flea and tick prevention:

• Your dog has tremors, wobbliness, or seizures
• Your dog vomits within an hour of taking the chew (they may not have absorbed the full dose)
• You find ticks on your dog despite being current on prevention (no product is 100%)
• Your dog has a skin reaction or unusual behavior change
• You’re not sure which products can be safely used together

The Bottom Line

All three products — NexGard, Bravecto, and Simparica Trio — are effective at killing fleas and ticks. They share the same drug class, the same FDA warning, and the same fundamental mechanism.

The right choice depends on your dog’s specific needs: Do you want the convenience of fewer doses (Bravecto)? The simplicity of all-in-one coverage (Simparica Trio)? Or a reliable monthly option that pairs with your existing heartworm prevention (NexGard)?

There’s no wrong answer among these three for most dogs. The wrong answer is no parasite prevention at all.

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Sources

1. FDA - FDA Alert: Isoxazoline Flea and Tick Products
2. American Heartworm Society - Heartworm Prevention Guidelines
3. Companion Animal Parasite Council (CAPC) - Parasite Prevalence Maps
4. Merck Veterinary Manual - Ectoparasiticides: Isoxazolines
5. VCA Animal Hospitals - Flea and Tick Prevention Comparison