Reactions to Ivermectin in Horses

Updated November 21, 2016

Ivermectin is an antibiotic designed to help horses resist a number of bacteria and other forms of infection. However, in some cases, instead of making your horse healthier, it can make your pal very sick. The best way to deal with this potential is to be very familiar with reaction to Ivermectin in horses so you can monitor your horse's reaction to the drug when he first receives it.


Ivermectin is designed to cure problems with lungworm. You can give Ivermectin to a horse as an oral paste or in the form of an injection. The antibiotic kills any worms in the horse's system and then the worms are passed out either via excretion or expulsion in phelgm.

Types of Allergic Reaction

In a study of more than 3,000 horses published in the Journal of the American Veterinary Medical Association, 366 horses had adverse reactions to Ivermectin. These reactions ranged from coughing, fever and colic to death. Some horses had swelling and stiffness at the injection site. The majority of the horses tested either experienced "midline pruritus" (serious itching and inflammation) or oedema (swelling due to liquid accumulation) on some part of the body.


Since Ivermectin can be administered in more than one way to horses, you should consult your veterinarian to see if one form of the medication is more likely to cause allergic reactions than another. Injections tend to create on-site problems, while the oral paste form of Ivermectin may be more likely to cause coughing and fever. However, you must consult a professional to determine if this is the case for your horse.

Time Frame

Most horses that experience allergic reactions to Ivermectin show symptoms fairly quickly--within a few minutes to 24 hours. However, the reaction can last from several days to several weeks, and the treatments are also very time consuming. You will have to monitor your horse closely if she has a reaction to ensure you are treating all the symptoms, since the few medications that may be used to treat Ivermectin reactions directly can cause seizures and are generally not recommended for use, according to The American Board of Veterinary Toxicology.


Ivermectin should be used in prescribed doses and by a veterinary professional. You should not use this medication to treat your horse unless it has been recommended by your veterinarian. Doses for horses are generally fairly small, so it is easy to overdose and create a severe reaction if you are not working under the supervision of a trained equine expert.

Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author