anthelmintic (drug) -- encyclopedia britannica

7/28/2019 Anthelmintic (Drug) -- Encyclopedia Britannica

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anthelmintic, any drug (/EBchecked/topic/171942/drug) that acts against infections caused by parasitic

worms (/EBchecked/topic/649101/worm) (helminths).

Helminths can be divided into three groups: cestodes, or tapeworms

(/EBchecked/topic/583137/tapeworm); nematodes (/EBchecked/topic/408450/nematode), or roundworms;

and trematodes, or flukes (/EBchecked/topic/211298/fluke). The helminths differ from other infectious

organisms in that they have a complex body structure. They are multicellular and have partial orcomplete organ (/EBchecked/topic/431855/organ) systems (e.g., muscular, nervous, digestive, and

reproductive). Several of the drugs used to treat worm infections affect the nervous system

(/EBchecked/topic/409665/nervous-system) of the parasite and result in muscle paralysis. Other drugs

affect the uptake of glucose (/EBchecked/topic/235853/glucose) and thus energy stores. All are chemical

agents and are generally administered orally, and many are used in both human and veterinary

medicine (/EBchecked/topic/627068/veterinary-medicine). No anthelmintic, however, is completely

effective, completely without toxic effect upon the host, or equally active against all worms.

Tapeworms attach to the intestinal tract by a sucker or a sucking groove on the head (scolex). Unlike the

nematodes and trematodes, tapeworms do not enter the host tissues (/EBchecked/topic/597008/tissue).

As a result, tapeworm infections in general are more easily treated than infections caused by worms

that penetrate host tissues. In addition, because tapeworms are confined to the intestinal tract, they

need not be killed by the drug, and the drug need not be absorbed when given by mouth. Thus, there

usually is a wider margin of safety for cestode anthelmintics than for anthelmintics used to treat worm

infections in sites other than the intestine. The term vermifuge is often applied to remedies that are

used to remove intestinal worms.

The primary drugs used for cestode infections (/EBchecked/topic/103879/cestodiasis) are albendazole

and praziquantel. Albendazole inhibits the uptake of glucose by the helminth and therefore the

production of energy. It has a spastic or paralytic effect on the worm. Praziquantel also produces

tetanus (/EBchecked/topic/588844/tetanus)-like contractions of the musculature of the worm. Unlike

albendazole, praziquantel is readily absorbed from the intestinal tract. It is a broad-spectrum

anthelmintic affecting both flukes and tapeworms.

Quinacrine, an early synthetic antimalarial later superseded, is often used as an anthelmintic for the

treatment of tapeworm infection in dogs (/EBchecked/topic/167647/dog), cattle(/EBchecked/topic/100077/cattle), and other animals (/EBchecked/topic/25501/animal).

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anthelmintic

Introduction (/EBchecked/topic/27270/anthelmintic) Cestode anthelmintics (/EBchecked/topic/27270/anthelmintic#toc309530)

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Treatment of roundworms is complicated by the fact that some live in blood

(/EBchecked/topic/69685/blood), lymphatics, and other tissues (filarial worms

(/EBchecked/topic/206771/filarial-worm)) and thus require use of drugs that are absorbed from the

intestinal tract and penetrate into tissues. Others are found primarily or solely in the intestinal tract

(intestinal nematodes). Diethylcarbamazine (/EBchecked/topic/162803/diethylcarbamazine) and

ivermectin, used for treating filarial worm infections, are absorbed from the intestinal tract. Blood levels

are reached quickly, and action against the microfilariae is rapid. A severe allergic or febrile reaction

due to the death of the microfilariae can follow the use of these drugs.

Like albendazole, mebendazole interferes with glucose uptake and consequently with the production of

energy. Mebendazole accumulates in the intestine and is used for treating l arge intestinal roundworms

(ascarids), hookworm (/EBchecked/topic/271350/hookworm-disease), and whipworm

(/EBchecked/topic/641889/whipworm) infections. It is well tolerated, but abdominal discomfort and

diarrhea (/EBchecked/topic/161659/diarrhea) can occur in patients with a severe infection.

Piperazine (/EBchecked/topic/461417/piperazine), introduced into human medicine

(/EBchecked/topic/372431/medicine) about 1950 and shortly thereafter into veterinary medicine, relaxes

the ascarids and pinworms (/EBchecked/topic/461262/pinworm) (oxyurids) of humans and domesticated

animals so that they are eliminated with the feces. Piperazine has been largely superseded by drugs

such as mebendazole and pyrantel pamoate.

Pyrantel pamoate causes spastic paralysis of helminth muscle. Most of the drug is not absorbed from

the intestinal tract, resulting in hi gh levels in the intestinal lumen. It is a drug of choice in treating

pinworm and is an alternative therapy for Ascaris (/EBchecked/topic/37797/ascariasi s) infection,hookworm, and trichostrongolosis.

Thiabendazole, which is structurally related to albendazole and mebendazole, is used primarily for the

treatment of several nematodes of cattle, horses (/EBchecked/topic/272156/horse), and sheep

(/EBchecked/topic/539405/sheep). Dithiazanine is another nematode anthelmintic used in veterinary

medicine; it is effective against heartworms and threadworms (/EBchecked/topic/593614/threadworm).

Levamisole is used in the treatment of lungworm (/EBchecked/topic/351620/lungworm) infections in

cattle. Phenothiazine (/EBchecked/topic/455623/phenothiazine), introduced in the 1930s, is still used

against the wireworm (Haemonchus contortus) of sheep and cattle.

Hygromycin is an antibiotic (/EBchecked/topic/27751/antibiotic) that may also be used as an

anthelmintic in the form of a feed additive to eliminate or reduce ascarids, nodular worms

(Oesophagostomum), and whipworms (Trichuris) of swine, and the large roundworms (Ascaridia) and cecal

worms (Heterakis) of poultry (/EBchecked/topic/472991/poultry).

Praziquantel is the most effective drug in treating infections caused by intestinal, liver, and lung flukes

and is the drug of choice in the treatment of schistosomiasis (/EBchecked/topic/527459/schistosomiasis)

(infections of blood flukes). Praziquantal causes contraction and spastic paralysis of the worm and also

damages the membranes of the worm, which activates host defense mechanisms.

1 (/EBchecked/topic/27270/anthelmintic) 2 (/related-topics/27270/related-topics-to-

anthelmintic) 3 (/topic/27270/contributors) Next (/related-topics/27270/related-

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