Historically, pyrantel (used in high doses) was the most common chemical employed to rid a horse of tapeworms. Praziquantel was used first in small animal practice and in the early 2000's became commercially available and FDA approved for equine use.

Praziquantel is effective only against cestodes, or tapeworms (Anoplocephala spp.) and none of the other worm types or external parasites. Because of this, praziquantel is currently marketed only in combination with macrocyclic lactones, such as ivermectin or moxidectin. The most common formulation of the equine product is the paste form.

Praziquantel acts by disrupting the tapeworm’s outer layer, making the worm incapable of maintaining a balanced equilibrium of body fluids and electrolytes.

Antibody titers have revealed that tapeworms infest a majority of horses in certain regions while in others, the prevalance is very low. There is currently debate as to whether this chemical should be used in regions in which the incidence of tapeworm infestation is low.

YOUR VET'S ROLE

The usefulness of any anthelmintic medication depends not only on the effectiveness of the drug against a particular parasite species, but also on the drug's pharmacology (how much of the chemical is exposed to the parasite in question and for how long), characteristics of the host animal (general health and immunity) and characteristics of the parasite (not only its susceptibility to the anthelmintic but also its location in the body and susceptibility at various life stages to the drug).

Your vet will advise you as to whether praziquantel is necessary in your region.

YOUR ROLE

Horse owners play a vital role in the use of anthelmintic drugs. All anthelmintic drugs should be administered as part of a targeted deworming program along with management techniques to reduce intake of infective parasites.

Random rotational use of dewormers without fecal testing is leading to parasite resistance and the rapid loss of effectiveness of this and other deworming compounds.