Ivermectin Dosing for Dogs

You know your dog feels his best when you see him leaping in the air and chasing a ball across the yard or stretched out for belly rubs after a long day. Preventive medicine can keep him healthy, including avoiding heartworms. Ivermectin is the active ingredient in many heartworm prevention pills as well as medications to stop severe itching.

Some parasites can make your dog scratch until his skin is raw and his fur falls out in clumps. Another can invade your dog's heart and lungs and if left unchecked can kill him. The drug ivermectin can both prevent and treat certain kinds of parasites, such as the mites that cause mange and heartworms. However, while ivermectin for dogs can be potentially lifesaving, it can also be toxic if given in too high a dose.

Ivermectin paralyzes and kills certain parasites by causing neurological damage. The drug is sold under a number of brand names for pets, including Ivomec for dogs. Normomectin for dogs is an injectable form of the drug. Ivermectin is also available in pill form and as an oral solution as well as a topical treatment rubbed onto the skin. While ivermectin is the active ingredient in several products for humans such as Sklice, which kills lice, ivermectin for flea treatment is not recommended

Dogs in all 50 states have become infected with heartworms, whose larvae are transmitted by the bite of a mosquito. Over about seven months, the heartworm larvae mature into full-grown worms that can be up to a foot long and wreak havoc internally. Heartworms may initially cause no symptoms, but as they grow, a dog will begin coughing as the worms crowd his lungs.

Because treating heartworms is difficult, vets focus on preventing them from infecting dogs in the first place. Ivermectin is the active ingredient in many heartworm prevention medications, including Heartgard Plus and Iverhart Plus. Dogs usually get one pill a month with a dose of 6 micrograms of ivermectin per kilogram of a dog's weight, according to petMD. For example, a 25-pound dog weighs about 11 kg and would get 66 micrograms of ivermectin for heartworm prevention.

Ivermectin is also used to treat infestations of two types of microscopic mites that cause mange's severe itching and loss of fur as they burrow under the skin. Sarcoptic mange, which is highly contagious, is caused by the Sarcoptes scabiei mite. Demodectic mange, caused by the Demodex mite, may result in more localized fur loss.

The dosage for ridding dogs of mites is far higher than for heartworm prevention. Sarcoptic mange is treated with 300 micrograms of ivermectin per kilogram of a dog's weight. The harder to treat demodectic mange requires 400 to 600 micrograms per kilogram.

Many dogs can tolerate doses of ivermectin up to 2,000 micrograms per kilogram but can overdose if more is mistakenly given. Just as the drug can kill parasites in small doses, it can poison dogs, causing a number of neurological symptoms. The first signs of trouble are dilated pupils, drooling, and unsteadiness. Severe toxicity can paralyze a dog's legs, cause seizures and tremors, and even put a pet in a coma.

Unfortunately, young dogs can be susceptible to ivermectin toxicity at doses as low as 100 micrograms per kilogram. Also, some breeds have a gene that can make them extremely sensitive to ivermectin and other drugs. Breeds that may carry the MDR1 or ABCB1 genes include collies, shelties, German and English shepherds, old English sheepdogs, and long-haired whippets, according to Healthy Pets. Dogs who are a mixed breed containing one of these types of dog may also be highly sensitive to ivermectin.

Caught early, ivermectin poisoning can be treated. If a topical form has been used, dogs may be decontaminated by giving them a bath. Those who have ingested too much ivermectin can be given activated charcoal or have vomiting induced. Dogs may also need to be intubated or put on a mechanical breathing machine if they have trouble breathing. Lipid emulsion therapy, a mixture of fats administered by IV, has also been helpful in treating dogs who have been severely poisoned.