4-[(3-Carboxy-2-hydroxynaphthalen-1-yl)methyl]-3-hydroxynaphthalene-2-carboxylic acid; 1-methyl-2-[(E)-2-thiophen-2-ylethenyl]-5,6-dihydro-4H-pyrimidine
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Pyrantel pamoate (under US Pharmacopoeia) or Pyrantel Embonate (under European Pharmacopoeia), is used as a deworming agent in the treatment of hookworms (all species) and roundworms (Ascaris lumbricoides, aka ascarids in humans) in domesticated animals such as horses, cattle, sheep, pigs, cats, dogs, and many other species. It is a combination of pyrantel and pamoic acid. Some drug companies pair pyrantel pamoate with praziquantel for tapeworms, and sometimes febantel for whipworms in order to provide more complete treatment for intestinal parasites in one dose.
It is also used for pinworm treatment for humans in many brands, including "Reese's Pinworm Medicine", "Pin-X", "Pin-Rid","PYRANTRIN" formally called "COMBANTRIN", "Anthel", "Helmintox", "Helmex".
Pyrantel pamoate is also commonly included in monthly administered chewable heartworm preventative tablets for dogs.
Pyrantel pamoate acts as a depolarizing neuromuscular blocking agent, thereby causing sudden contraction, followed by paralysis, of the helminths. This has the result of causing the worm to "lose its grip" on the intestinal wall and be passed out of the system by natural process. Since Pyrantel is poorly absorbed by the host's intestine, the host is unaffected by the small dosage of medication used. Spastic (tetanic) paralyzing agents, in particular pyrantel pamoate, may induce complete intestinal obstruction in a heavy worm load. This obstruction is usually in the form of a worm impaction and happens when a very small, but heavily parasitized animal is treated and tries to pass a large number of dislodged worms at once. Worms usually pass in normal stool or with diarrhea, straining, and occasional vomiting.
Pyrantel pamoate is considered a Pregnancy category C drug for use during pregnancy for humans, but is in category A for canines and felines. Pyrantel is considered safe to use in nursing animals.