Ivermectin dosage reference for cats (Heartgard for Cats)

Ivermectin (sold for cats as Heartgard for Cats chewables and Acarexx ear suspension) is a macrocyclic lactone antiparasitic. In cats its labeled oral use is monthly heartworm prevention and hookworm control; ear mites are treated with an ivermectin ear product, and higher-dose oral or injectable use for mites or mange is off-label and belongs with your veterinarian.

Label Weight Bands for Heartworm Prevention

The HEARTGARD for Cats label sets a minimum of 24 mcg of ivermectin per kg (10.9 mcg per lb), given once a month, and lists one chewable per month by weight:

Because one chewable covers a whole band, a cat receives at least 24 mcg/kg, and more if it is light for its band. The label reports a 30-fold safety margin over that minimum in a single-dose tolerance study, and recommends the chewables for cats 6 weeks of age and older.

Mite and Mange Doses Are for Your Veterinarian

Ear-mite and mange protocols use roughly ten times the heartworm dose or a different route entirely, and cats tolerate those doses less predictably. This page deliberately does not list them. Ask your veterinarian to choose the product, dose, and any repeat treatment.

The formulation matters as much as the number. Otic products, cat heartworm chewables, dog heartworm chewables, injectable solutions, and concentrated horse or cattle products are not substitutes for one another. A small decimal or dilution error can be clinically important in a cat.

How to Give Ivermectin to Your Cat

Give the complete monthly dose your veterinarian prescribes: one whole chewable for cats up to 15 lb (by label band); for cats over 15 lb your vet chooses the combination of chewables. Give it once a month on about the same date. It can be offered by hand or in a little food, or broken into pieces if you need to give it by mouth; watch to make sure the whole dose is eaten. The label recommends a heartworm test before starting. For ear mites, use the otic product exactly as prescribed. Use only the exact cat-specific product supplied or identified by the prescribing veterinarian. Never convert, dilute, or measure a dog chewable or a large-animal horse or cattle formulation at home; concentration errors can be dangerous in cats.

The label notes that food should be available on the day of dosing, because a fasted cat may absorb less. It may interact with Spinosad (increased ivermectin toxicity risk), Ketoconazole and other P-glycoprotein inhibitors (increased ivermectin levels), Other macrocyclic lactones (additive toxicity), and Benzodiazepines (may mask early neurotoxicity signs).

Side Effects and Safety

Common side effects include Transient lethargy, Decreased appetite, Drooling (if given orally and tastes the solution), and Mild diarrhea. More serious side effects can occur, such as Neurotoxicity (ataxia, tremors, blindness, seizures, coma), Hypersalivation and vomiting (early toxicity sign), Death (at toxic doses), and Severe allergic reaction.

When to Call the Vet

If your cat experiences any of the following, contact your veterinarian or an emergency clinic immediately:

• 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

Frequently Asked Questions