Short answer: Simparica Trio (sarolaner/moxidectin/pyrantel) is FDA-approved for healthy dogs 8 weeks and older and 2.8 lb or more. The main warning is the same as NexGard – rare neurologic events in roughly 0.01-0.03% of dogs. Dogs with seizure history should consider a non-isoxazoline option.
🚨 Red flag — call your vet now if: your dog is a collie, Australian shepherd, Shetland sheepdog or other herding breed without MDR1 genotype testing; has a history of seizures; or weighs less than 2.8 lb.
What you should actually do
- Three drugs in one chew: sarolaner (fleas/ticks, isoxazoline), moxidectin (heartworm), pyrantel (roundworms + hookworms).
- Pre-approval field study (Zoetis, n=559) showed the most common adverse events were vomiting (3.8%), diarrhea (3.2%), and lethargy (1.6%) – mostly self-limiting in 24-48 hours.
- FDA’s 2018 isoxazoline-class warning applies: rare tremors, ataxia, or seizures – report to FDA-CVM if seen.
- Onset of action: fleas dead within 4 hours, ticks within 8-24 hours, intestinal worms within 24-48 hours.
- Do NOT use in puppies under 8 weeks, dogs under 2.8 lb, or in collies/herding breeds with known MDR1 mutation without prior genotyping (moxidectin sensitivity).
MDR1 (multidrug resistance gene 1) deficiency is common in collie-type breeds and causes a defective blood-brain barrier. Affected dogs cannot pump ivermectin or moxidectin out of the central nervous system, and a normal dose can cause coma or death. About 75% of rough collies, 50% of Aussies, and 15% of border collies carry at least one MDR1 mutation – testing is available from the WSU lab for around $60 and is recommended before any macrocyclic lactone exposure.
For dogs that pass MDR1 testing or are non-herding breeds, Simparica Trio’s combined coverage (fleas, ticks, heartworm, GI worms) is one of the broadest single-dose preventives available. Vomiting in the first 24 hours after dosing is the single most common complaint and is usually managed by giving the chew with a meal.
Dig deeper
⚕️ Medical Disclaimer
The information on this page is intended for educational purposes only and does not replace a hands-on veterinary examination. Drug doses depend on your dog’s complete clinical picture, concurrent medications, and the exact product formulation. Always confirm dosing with your veterinarian before administering any medication, and contact a 24-hour veterinary emergency service or animal poison control immediately if you suspect a medication overdose or adverse reaction. Editorial standards: every drug dose published on PuppaDogs is cross-checked against multiple authoritative veterinary references and reviewed by PuppaDogs Veterinary Editorial Team before publication.
