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Ivermectin for horses is one of the most effective methods for the treatment and prevention of parasites. The drug works to combat 35 different parasitic organisms, including strongyles, multiple types of worms, and bots. The worms that it can treat and control include pinworms, lungworms, and intestinal hairworms. It is considered safe for use in all horses, although the manufacturers recommend against using it in animals that are meant for food. Ivermectin paralyzes the neurotransmitter gamma-amino-butyric acid (GABA) in parasites. This acid is unique to parasitic organisms, and therefore a typical ivermectin dose will not affect vertebrates such as horses. It can prevent new infections from parasites and also works to destroy active infections.
Owners can purchase ivermectin for horses in a paste form. It is often sold in a plastic syringe, which will contain enough of the drug for one or more fully grown horses. To administer the drug, the syringe tip should be inserted into the horse’s mouth. The paste is then injected onto the back of the animal’s tongue. Owners are often advised to then hold the horse’s head up so it can’t spit the medicine out. It is considered very difficult to cause an overdose when using ivermectin for horses. Animals have been known to ingest up to nine times the recommended dosage with no side effects. Administration of ivermectin for the control of parasites can begin when the horse is as young as six to eight weeks of age.
The drug is so effective at controlling parasites that veterinarians often recommend swapping it out for another treatment type occasionally. The concern is that parasites will eventually develop a resistance to ivermectin for horses, rendering it ineffective. At the same time, vets caution against rotating dewormers too frequently and say that this could cause parasites to develop resistances to multiple drugs at once. The recommended course of action is to work closely with a vet when administering a deworming treatment program for horses.
The use of ivermectin for horses has occasionally been known to cause side effects. Swelling and itching have happened in some horses after they’ve been treated with ivermectin for thread neckworm microfilariae. It is believed that the reactions were due to large numbers of the microfilariae dying off all at once. Ivermectin is considered extremely safe for horses, but humans are cautioned to wash their hands after handling the drug. Used ivermectin syringes should not be disposed of in a water source because of the potential to harm or kill invertebrates in the water.