Pyrantel pamoate is the compound in most paste and liquid deworming formulations whereas the tartrate salt is the compound contained in continuous dewormers.

Pyrantels mimic the activity of acetylcholine, a natural neurotransmitter that causes muscle contraction. In susceptible worm species, the pyrantels cause irreversible muscle contraction, resulting in rigid paralysis and death. Pyrantel causes a rapid die-off of susceptible worms.

Pyrantel does not penetrate the intestinal wall and so does not kill encysted strongyles.

There is growing small strongyle resistance to this compound. It is quite effective against pinworms. At high doses it has some activity against tapeworms but it is not considered as effective as praziquantel.

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 suggests pyrantels as the best choice deworming compound based on results of fecal diagnostic testing and identification of specific parasites affecting your horses.

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.