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Pyrantel: A Safe and Effective Pinworm Treatment

The Bottom Line

Pyrantel is an important drug for the control of intestinal worms in people and animals. It is estimated that close to 1 billion people are infested with intestinal worms globally. Pyrantel is a safe, effective, and inexpensive treatment for intestinal worms, and usually cures the condition after a single dose. It has very few side effects and is not known to cause toxicity in humans.

The Full Story

You might not have heard of it before, but pyrantel is a drug used to treat a serious condition suffered by millions of people every year. That condition is intestinal worms. The worms (helminths) cause symptoms ranging from abdominal pain and loss of appetite to dysentery. Drugs used to combat intestinal worms are known as anthelmintics.

Intestinal worms are transmitted through soil that is contaminated with feces containing the eggs of worms. When a person or animal ingests soil (from unwashed hands or food), the eggs hatch in the intestines and lead to illness. Worms can also be transmitted to humans by handling pets, such as dogs and cats that have not been treated for worms. Pet birds can also carry worms. Since intestinal worms can be transmitted from animals to people, they are considered "zoonotic" infestations.

According to the World Health Organization, soil-transmitted worm infestations afflict close to 1 billion people worldwide. About 10% of the population in the developing world is affected. In heavily infested areas, more than 50% of people can have intestinal worms. People in developing regions are at higher risk due to poor sanitation. Worm infestations can follow contact with household pets and other animals such as horses, cattle, sheep, goats, pigs, and llamas. Dogs and cats entering animal shelters are routinely treated for worms using pyrantel or other anthelmintic medications. Since an estimated 68% of households in the US own at least one pet, control of intestinal worms in pets has become an essential safeguard in preventing transmission to humans. In addition, children can pick up worm infestations by playing in dirt contaminated with feces and not washing their hands before eating or putting their hands in their mouths. If a person is diagnosed with intestinal worms, the entire household should be treated to prevent spread and reinfestation.

Pyrantel is a safe, effective, and inexpensive treatment for several types of intestinal worms. It has been in use since the mid-1970s. The most common form of pyrantel for human and veterinary use is pyrantel pamoate. The drug is FDA-approved for pinworm infestations. It is also effective for roundworms, hookworms, and whipworms. It is available without a prescription as a generic medication or under brand names such as Antiminth, Reese's Pinworm Medicine, Ascarel, and Pin-X. Pyrantel for veterinary use is found in products like Heartgard Plus, Strongid-T, and Nemex. Pyrantel cures worm infestations by paralyzing the worms, which then release from the intestines and travel out of the body in the stool.

Pyrantel has the advantage of being usually effective after a single oral dose. In some cases, a second dose might be needed 2 weeks later. Another good thing about pyrantel is that it is not well absorbed into the body from the intestines, so it produces very few side effects. At most, mild symptoms such as nausea, diarrhea, headache, and dizziness might be expected. In very rare cases, pyrantel has caused temporary worsening of myasthenia gravis (resulting in muscle weakness) due to the drug's effect on nerve receptors controlling muscular movements. It is important to note that people of Asian descent are at higher risk for this type of reaction to pyrantel (see "This Really Happened"). Even with an overdose of pyrantel, no toxicity is expected. In fact, there are no reports of serious human poisoning with pyrantel in the medical literature.

If you have questions about an adverse reaction or possible overdose of pyrantel, immediately check the webPOISONCONTROL® online tool or call Poison Control at 1-800-222-1222 for help 24 hours a day, every day.

For More Information

Intestinal worms. Geneva: World Health Organization [cited 2020 May 26].

Parasites - ascariasis. Atlanta: Centers for Disease Control and Prevention; 2018 Feb 15 [cited 2020 May 28].

Parasites - enterobiasis (also known as pinworm infection). Atlanta: Centers for Disease Control and Prevention; 2019 Aug 5 [cited 2020 May 28].

Pearson RD. Pinworm infection (enterobiasis, oxyuriasis). Kenilworth NJ: Merck & Co.; 2019 Mar [cited 2020 May 26].


References

Bescansa E, Nicolas M, Aguado C, Toledano MA, Viñals M. Myasthenia gravis aggravated by pyrantel pamoate [letter]. J Neurol Neurosurg Psychiatry. 1991 Jun;54(6):563.

Drugs for parasitic infections. Treatment Guidelines from The Medical Letter. 2013 Aug 1;11 (Suppl):e1-31.

Kopp SR, Kotze AC, McCarthy JS, Traub RJ, Coleman GT. Pyrantel in small animal medicine: 30 years on. Vet J. 2008 Nov;178(2):177-84.

Pyrantel. In: Plumb DC. Plumb's veterinary drug handbook. 9th ed. Stockholm (WI): Pharma Vet Inc.; 2018:1013-6.

Pyrantel management. In: Poisindex System [database on the internet]. Greenwood Village (CO): Truven Health Analytics [cited: 30 May 2020].

Raza A, Rand J, Qamar AG, Jabbar A, Kopp S. Gastrointestinal parasites in shelter dogs: occurrence, pathology, treatment and risk to shelter workers. Animals (Basel). 2018 Jul;8(7):108.

Savioli L. Preventive anthelmintic chemotherapy – expanding the armamentarium [editorial]. N Engl J Med. 2014 Feb 13;370(7):665-6.

Shen C, Li M, Zhao X, Cui L. An ocular myasthenia gravis attack after oral pyrantel pamoate: an unusual case report. Medicine. 2019 Jul 5;98(27):e16321.

Poisoned?

Call 1-800-222-1222 or

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Prevention Tips

  • Clean up animal waste.
  • Wash hands before eating or preparing food.
  • Wash hands after contact with animals or feces.
  • If a person is diagnosed with intestinal worms, the entire household should be treated to prevent spread and reinfestation.
  • When using an OTC anthelmintic, follow all instructions. Contact a healthcare professional if one dose is ineffective or if more than minor side effects occur.
  • Keep all medications in child-resistant packaging and away from children and pets.

This Really Happened

Case 1. A 4-year-old Asian girl was treated with a non-prescription pinworm medication containing pyrantel pamoate. Two days later, she was seen at a clinic because of a drooping eyelid and periodic double vision. She was diagnosed with ocular myasthenia gravis (OMG), which responded to usual treatment for that condition. She did not receive pyrantel again, and the problem did not recur (from Shen et al., 2019).

Case 2. A 72-year-old man received a single dose of pyrantel pamoate (1000 mg) for roundworm infestation. Within a few hours, he noticed fatigue when walking and also when he chewed. Drooping eyelids, fatigue, limb weakness, and difficulty breathing followed. The symptoms improved gradually with several months of prednisone treatment. It was likely that pyrantel had aggravated an undiagnosed case of myasthenia gravis in this man (from Bescansa et al., 1991).