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Antihelmintics are drugs used to kill parasitic worms (from the Greek word helmins, worm). These preparations are also called vermicides.

Worm infestations are among the most common parasitic diseases of man. Often the life cycle of the worm begins when a child playing in dirt ingests the eggs of the worm. The egg hatches in the child's digestive tract and the worms begin their unending quest to reproduce, make more eggs, and infect more hosts.

Parasitic worms may be either round (called nematodes), or have a segmented, flat configuration (called cestodes). Worms are most problematic in areas where sanitation is poor.

The most common parasitic worm infestation in nontropical climates is by the pinworm (Enterobias vermicularis), which is highly infectious and may affect an entire family before the infection is diagnosed. At any time, up to 20% of the childhood population has pinworms and may jump to 90% among children who are institutionalized, as in an orphanage.

Other roundworm infections are by the hookworm and whipworm, either of which can gain entrance to the body by penetrating the skin of a bare foot. Trichinosis derives from eating raw or undercooked pork containing the worm larva.

Flat, segmented worms, also called tapeworms, can originate in raw beef, pork, or fish. These worms attach their heads to the walls of the intestine and shed square segments that are packages of eggs.

Most roundworm infestations can be cleared by taking pyrantel pamoate, a drug for sale over the counter. It was developed in 1972 as a prescription drug. Because it is given in the form of a pill or syrup in a single dose, based on body weight, without serious side effects, pyrantel was approved for nonprescription sale. This medication relaxes the muscles that the worm holds on to on the intestinal wall so the worm is passed out with a normal fecal movement.

Other, more potent drugs are available by prescription to treat worm infections. They include piperazine, tetrachloroethylene, and thiabendazole for roundworms, and niclosamide for tapeworms.

See also Parasites.

Larry Blaser

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