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PetDosageChart

Heartgard Plus (Ivermectin / Pyrantel) Dosage for Dogs

Antiparasitic combination ⏱ Onset: N/A (preventive) ⏳ Duration: 30 days

This dosage information is for educational purposes only. Always consult your veterinarian before giving any medication to your pet. Dosages may vary based on your pet's health conditions, other medications, and individual factors.

Content reviewed by licensed veterinarians. This information is sourced from veterinary drug references including Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

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Heartgard Plus Dosage Chart for Dogs by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
5 lbs (2.3 kg) 0mg 0mg 0mg once monthly
10 lbs (4.5 kg) 0mg 0mg 0mg once monthly
15 lbs (6.8 kg) 0mg 0mg 0mg once monthly
20 lbs (9.1 kg) 0mg 0mg 0mg once monthly
25 lbs (11.3 kg) 0mg 0mg 0mg once monthly
30 lbs (13.6 kg) 0mg 0mg 0mg once monthly
40 lbs (18.1 kg) 0mg 0mg 0mg once monthly
50 lbs (22.7 kg) 0mg 0mg 0.5mg once monthly
60 lbs (27.2 kg) 0mg 0mg 0.5mg once monthly
70 lbs (31.7 kg) 0mg 0mg 0.5mg once monthly
80 lbs (36.3 kg) 0mg 0mg 0.5mg once monthly
90 lbs (40.8 kg) 0mg 0mg 0.5mg once monthly
100 lbs (45.4 kg) 0.5mg 0.5mg 0.5mg once monthly
120 lbs (54.4 kg) 0.5mg 0.5mg 0.5mg once monthly
150 lbs (68 kg) 0.5mg 0.5mg 1mg once monthly

What is Heartgard Plus (Ivermectin / Pyrantel) used for in dogs?

heartworm prevention roundworm treatment hookworm treatment

How to give Heartgard Plus to your dog

Give Heartgard Plus on the same day each month, year-round. It is a beef-flavored chewable that most dogs eat willingly. A heartworm test is required before starting. At the very low doses used in Heartgard, ivermectin is generally safe even for most MDR1-positive breeds, but consult your vet.

Available Forms

chewable tablet

Give with Food?

Yes — give with food

Side effects of Heartgard Plus in dogs

Common side effects

vomiting
diarrhea
decreased appetite
lethargy

Serious side effects

  • allergic reaction
  • tremors (rare)
  • seizures (rare, MDR1 breeds at higher doses)

When to call the vet

Call your vet immediately if your dog shows any of these signs:

  • Vomiting within 1 hour of dosing
  • Your dog misses more than one monthly dose
  • You moved from a non-endemic to an endemic heartworm area
  • Any neurological signs (tremors, incoordination)
  • Your dog tests positive for heartworm

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Sentinel

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Antiparasitic

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Sources & References

The dosage information on this page is compiled from the following veterinary and pharmaceutical references:

  • Plumb's Veterinary Drug Handbook — the standard veterinary pharmacology reference used by veterinarians worldwide.
  • Merck Veterinary Manual — a trusted, peer-reviewed resource for veterinary professionals and pet owners.
  • DailyMed (FDA Drug Labels) — official FDA-approved drug labeling and prescribing information for Ivermectin / Pyrantel.

Frequently Asked Questions

Is Heartgard enough for my dog?
Heartgard Plus prevents heartworm and treats roundworms and hookworms, but it does NOT protect against fleas, ticks, or other external parasites. Most dogs need a flea/tick preventive (like NexGard) in addition to Heartgard. Your vet can recommend a complete parasite prevention plan.
What happens if I miss a month of Heartgard?
If you miss one month, give the dose as soon as you remember and resume the monthly schedule. If you miss more than one month, contact your vet — your dog may need to be tested for heartworm before restarting, as the preventive only kills larvae acquired in the previous 30 days.
Can I give Heartgard to Collies?
Yes. At the very low ivermectin doses used in Heartgard (6 mcg/kg), it is considered safe for Collies and other MDR1-positive breeds. The ivermectin toxicity risk in these breeds occurs at much higher doses (300+ mcg/kg), far above what Heartgard contains.
Does my dog need Heartgard year-round?
The American Heartworm Society recommends year-round heartworm prevention in all areas. Even in colder climates, unpredictable warm spells can allow mosquitoes to transmit heartworm. Year-round prevention is the safest approach.

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