Ivermectin is a common deworming medication used in dogs and cats to treat a variety of different diseases. It is one of the most widely used medications for preventing heartworm infection in cats and has been approved for use in cats since 1996.
The most well-known brand of heartworm prevention medication that contains ivermectin is Heartgard. When used as a heartworm prevention medication, ivermectin is typically used at a relatively low dosage range based on the size of the animal. For example, The usual dose of Heartgard for cats 5 pounds or less is 55 micrograms of ivermectin per dose and 165 micrograms for cats 6 to 15 pounds.
Ivermectin to Treat Heartworm Infection and Heartworm Disease
Ivermectin is also used in the so-called slow-kill or soft-kill method of heartworm treatment—although this is a bit of a misnomer. Ivermectin does not directly kill adult heartworms, but it does kill the microfilaria (larval form) of the heartworm. By killing the microfilaria, ivermectin prevents additional worms from maturing and occupying the heart and blood vessels. The adult heartworms already present there eventually die with time as the natural course of their life comes to an end.
In most cases, monthly dosages of ivermectin used to treat heartworm infection and prevent heartworm disease are the same. However, there is a higher risk of complications when a cat is infected with heartworms because of the presence of heartworms.
It is also important to remember that this method of heartworm treatment leaves allows adult worms to remain in the heart and blood vessels for a long time, sometimes for years. During that time, these heartworms continue to damage the heart and lungs.
Ivermectin is still one of the best medicinal treatments of heartworm infection for most cats. There are other methods of removing heartworm infection, such as surgery.
Dosage for Cats
In healthy cats, ivermectin is safe. Overdose can occur when pet owners administer ivermectin products for livestock on their cats in an attempt to save money.
A cat's toxic exposure can occur if the cat has more than 2.5 milligrams per kilogram (or for every 2.2 pounds of the cat's weight). A cumulative effect can develop in cats who receive several doses. If your cat has been exposed to a toxic level of ivermectin, symptoms may develop within 10 hours of ingestion.
Ivermectin for Treatment of Other Parasites
Besides preventing and treating heartworm disease, ivermectin is also used widely to treat other types of parasites. These include:
- Demodex, the mite responsible for causing demodectic mange
- Hookworms (Ancylostoma tubaeforme and Ancylostoma braziliense)
- Roundworms (Toxocara cati and Toxascara leonina)
- Ear mites (Otodectes cynotis)
- Lungworms (Capillaria and Aelurostrongylus abstrusus)
Ivermectin can be used to treat ear mites either systemically as an oral medication or an injection. It is also available as a topical medication in a medication known as Acarexx which is applied directly inside of the ear canal.
When using ivermectin to treat the other parasitic infections, it is used systemically at varying doses, depending on the type of parasite. In most cases, the dosages used for eradication of these parasites is much higher than the dosage used for heartworm prevention.