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Heartgard (Ivermectin) Dosage for Cats

Macrocyclic Lactone Antiparasitic ⏱ Onset: 4-8 hours ⏳ Duration: Varies by parasite; heartworm prevention lasts approximately 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 Dosage Chart for Cats by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
3 lbs (1.4 kg) 0mg 0.5mg 0.5mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
4 lbs (1.8 kg) 0mg 0.5mg 0.5mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
5 lbs (2.3 kg) 0mg 0.5mg 1mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
6 lbs (2.7 kg) 0mg 0.5mg 1mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
7 lbs (3.2 kg) 0mg 0.5mg 1.5mg (22 × 0.068mg) Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
8 lbs (3.6 kg) 0mg 0.5mg 1.5mg (22 × 0.068mg) Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
9 lbs (4.1 kg) 0mg 1mg 1.5mg (22 × 0.068mg) Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
10 lbs (4.5 kg) 0mg 1mg 2mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
12 lbs (5.4 kg) 0mg 1mg 2mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
14 lbs (6.3 kg) 0mg 1.5mg (22 × 0.068mg) 2.5mg (37 × 0.068mg) Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
16 lbs (7.3 kg) 0mg 1.5mg (22 × 0.068mg) 3mg (44 × 0.068mg) Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
18 lbs (8.2 kg) 0mg 1.5mg (22 × 0.068mg) 3.5mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
20 lbs (9.1 kg) 0mg 2mg 3.5mg Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention
25 lbs (11.3 kg) 0.5mg 2.5mg (37 × 0.068mg) 4.5mg (66 × 0.068mg) Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention

What is Heartgard (Ivermectin) used for in cats?

Ear mite treatment (Otodectes cynotis) Heartworm prevention Intestinal parasite treatment Demodectic mange (off-label) Notoedric mange (off-label)

How to give Heartgard to your cat

Ivermectin administration in cats varies by formulation. For heartworm prevention, use cat-specific products as directed. For ear mites, your vet may administer an injection or prescribe topical ear drops. If oral ivermectin is prescribed, it is usually the diluted injectable solution given by mouth using a precise syringe. Mix with a small amount of wet food to mask the taste. NEVER attempt to dose from large-animal (horse/cattle) formulations. Follow your vet's dosing instructions exactly—even small errors can be dangerous in cats due to the narrow safety margin.

Available Forms

Injectable solution (used orally or by injection), Topical (otic), Oral paste

Give with Food?

Yes — give with food

Side effects of Heartgard in cats

Common side effects

Transient lethargy
Decreased appetite
Drooling (if given orally and tastes the solution)
Mild diarrhea

Serious side effects

  • Neurotoxicity (ataxia, tremors, blindness, seizures, coma)
  • Hypersalivation and vomiting (early toxicity sign)
  • Death (at toxic doses)
  • Severe allergic reaction

When to call the vet

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

  • Wobbliness, tremors, or inability to walk (possible neurotoxicity)
  • Dilated pupils or apparent blindness
  • Seizures or loss of consciousness
  • Excessive drooling or vomiting within hours of dosing
  • Severe lethargy or unresponsiveness

Related Medications for Cats

Topical antiparasitic (avermectin)

Revolution

Selamectin

For flea prevention

View dosage chart
Anticonvulsant / Analgesic

Neurontin

Gabapentin

For pain management

View dosage chart
Antihistamine

Benadryl

Diphenhydramine

For allergies

View dosage chart
NK1 receptor antagonist / Antiemetic

Cerenia

Maropitant

For vomiting

View dosage chart

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.

Frequently Asked Questions

Is ivermectin safe for cats?
Ivermectin can be safe for cats when used at the correct dose, but cats have a narrower safety margin than dogs. The heartworm prevention dose (0.024 mg/kg monthly) is very safe. Higher doses used for mange or ear mites (0.2-0.4 mg/kg) carry more risk and should only be administered by or under the direct supervision of a veterinarian. Never use ivermectin products labeled for large animals (cattle/horses) on cats, as the concentration makes accurate dosing nearly impossible and overdose is common.
Can ivermectin treat ear mites in cats?
Yes, ivermectin is very effective against ear mites (Otodectes cynotis) in cats. It can be given as a subcutaneous injection (0.2-0.4 mg/kg), applied topically in the ear canal, or given orally. A single treatment often resolves the infestation, though a second dose 2 weeks later may be recommended to kill newly hatched mites. Your vet will determine the best route of administration for your cat.
What are the signs of ivermectin toxicity in cats?
Signs of ivermectin toxicity include excessive drooling, vomiting, wobbliness (ataxia), tremors, dilated pupils, blindness, disorientation, inability to stand, seizures, and in severe cases, coma and death. Toxicity typically occurs within 4-12 hours of an overdose. If you suspect your cat has received too much ivermectin, seek immediate emergency veterinary care. There is no specific antidote, but supportive care (IV fluids, anti-seizure medication) can be life-saving.
How does ivermectin for cats differ from the dog version?
Cats generally have a narrower safety margin with ivermectin than dogs. The heartworm prevention dose is similar (0.024 mg/kg), but cats are more sensitive to higher therapeutic doses. Cat-specific products are formulated at appropriate concentrations. Dog-specific chewable heartworm preventatives should not be given to cats, as the formulation and flavorings differ. Always use cat-labeled ivermectin products.
Can I use horse ivermectin paste on my cat?
NEVER use horse or cattle ivermectin products on cats. These products are formulated at extremely high concentrations (1.87% paste, 1% injectable) designed for animals weighing hundreds of kilograms. It is virtually impossible to accurately measure a safe cat dose from these products, and even a tiny error can deliver a fatal overdose. Always use veterinary-prescribed, cat-appropriate ivermectin formulations.

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