Ivermectin Dosing for Dogs

By Colleen O'Brien

Ivermectin is a broad-spectrum prescription drug used to prevent and control the infestation of parasites in dogs. It's prescribed under a variety of brand names including Ivomec, Zimectrin, Heartgard and Iverhart. If your dog is healthy, it's generally safe to administer medications prescribed by a vet, although it's particularly important to give your dog the correct dose.


Although ivermectin has no effect on fleas and ticks, it is used to treat intestinal worms (except tapeworms), ear mites and skin conditions caused by parasites. It affects the nervous system of a parasite and paralyzes it. The parasite dies when it can no longer feed off of the dog. It's available in several forms, so it can be administered orally by pill, chewable tablet or liquid. It can also be injected.


Ivermectin is used to treat ear mites and mange, which is a skin disease that occurs when mites burrow under the skin and cause infection. It can be used monthly to prevent heartworm. It's also FDA-approved for use in treating heartworm once it's diagnosed, but it kills only the larval heartworm, so it can keep the disease from progressing. It does not kill the adult heartworm, though ivermectin can shorten its lifespan.


The dosage of medication administered depends on the weight of the dog. If it's being used to treat heartworm, the dosage is much lower than if it's being used to treat parasitic infections. For use as a heartworm preventative, the dosage is .0015 to .003mg per pound, administered monthly. Many manufacturers of ivermectin for dogs offer a beef-flavored chew, to make it easier for dogs to swallow. To treat parasites, the dosage is .15mg per pound. For a dog weighing 30 lbs., for example, the dose would be 4.5mg. Depending on the severity of the infection, this may be repeated until the parasites are completely gone.


The dosage necessary to treat gastrointestinal or skin parasites can be up to 100 times higher than the dosage to treat heartworm, so it's critical to give your dog the appropriate amount for his health issue. At low levels, ivermectin is safe and side effects are rare. At higher levels, it can cause blindness and neurological problems. Watch your dog for dilated pupils and an unsteady gait, which can quickly progress to paralysis and death if not addressed immediately.


It's important to administer a heartworm preventative regularly because heartworm disease, though preventable, is fatal if not treated in time. If a dog is bitten by an infected mosquito, worms grow in the bloodstream and settle in the heart, causing certain death if not addressed. Even when heartwom is diagnosed, treatment takes several weeks, and it is very uncomfortable for the dog. By the time the dog exhibits outward symptoms of heartworm disease, it may be too late.


Collies, Australian shepherds and sheepdogs are genetically predisposed to side effects from certain drugs, including ivermectin. Although dosages for heartworm treatment are very low, be sure to follow your vet's instructions carefully to avoid overdosing your pet. This medication should not be administered with tranquilizers or flea and tick preventatives. This can cause sedation and other negative neurological effects. Seek veterinary attention immediately if your dog exhibits an adverse reaction after taking the medication.