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Macrocyclic Lactone Antiparasitic · For Cats

How much Ivermectin (Heartgard) can I give my cat?

Standard Ivermectin dose for cats is 0.2 mg per kg (0.09 mg per lb), given Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention. Use the calculator below for your cat's exact weight, or jump to the weight-by-weight chart.

Onset
4-8 hours
Duration
Varies by parasite; heartworm prevention lasts approximately 30 days
Class
Macrocyclic Lactone Antiparasitic

Calculator estimate from Plumb’s Veterinary Drug Handbook. Not yet vet-reviewed — see our methodology .

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. Sourced from Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

Dosage Calculator · 01

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Heartgard dose by cat weight

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Dosage Chart · 02

Heartgard dosage for cats by weight

Scroll sideways to see full table

Weight Low Dose Standard Max Safe 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

Common Uses · 03

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)

Administration · 04

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 · 05

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 — call your vet

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

Emergency · 06

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

For Dogs

Looking for Ivermectin dosage for dogs?

View the Ivermectin dosage chart and calculator for dogs.

Related · 08

Related medications for cats

Sources · 09

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.

Read more about our methodology and how we calculate dosages.

Transparency · 11

How this page was made

Sourced from Plumb's Veterinary Drug Handbook, the reference used in US vet schools. Every dose, frequency, and tablet count on this page is generated from that data, then checked against the published references below.

Sources cited
  • Plumb's Veterinary Drug Handbook
  • Merck Veterinary Manual
Calculator formula
Doses scale linearly from a standard basis of 0.2 mg per kg (0.09 mg per lb) of body weight, given Single dose for ear mites (may repeat in 2 weeks); monthly for heartworm prevention. The calculator multiplies that basis by your cat's weight and rounds to the closest available tablet size.
Last-reviewed status
Automated from Plumb’s, not yet vet-reviewed.

More on our methodology and editorial process — how we source, calculate, and review cats dosage data.

Frequently Asked · 07

Questions about this medication

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.

Safety · 10

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