Cestode infections, drugs

Agents used in the treatment of cestodal infections include praziquantel (see Section Vll.a.l), niclosamide and the benzimidazoles such as albendazole and mebendazole (see Section vn.b.l). Niclosamide and praziquantel are effective against Taenia solum (pork tapeworm). Taenia saginata (beef tapeworm). Taenia latum (fish tapeworm) and Hymenolepis nana (dwarf tapeworm). Praziquantel is a second choice drug after albendazole for cys-ticercosis caused by Taenia solum. Albendazole and mebendazole are alternatives. 

Praziquantel is effective in the treatment of schistosome infections of all species and most other trematode and cestode infections, including cysticercosis. The drug s safety and effectiveness as a single oral dose have also made it useful in mass treatment of several infections. 

Three major groups of helminths (or worms), the nematodes, trema-todes and cestodes, infect humans. As in all antibiotic regimens, the anthelminthic drugs (Figure 36.1) are aimed at metabolic targets that are present in the parasite but are either absent from or have different characteristics than those of the host. Figure 36.2 illustrates the high incidence of helminthic infections. 

Fenbendazole (18) This drug shows high activity against Moniezia spp. in sheep (5-25 mg/kg) and calves (10-15 mg/kg) and, therefore, finds wide usage in the treatment of major nematode and a few cestode infections in above animals [176]. At a dose of 100 mg/kg, both fenbendazole and oxfendazole had no lethal effects on 10 week old cysticerci of T. saginata in calves [189]. 

Although a number of salicylanihde anthelmintics have been developed, most of them find use in the treatment of cestode and trematode infections in domestic animals. Niclosamide (4) is the only drug which has been extensively used to cure cestode infections in human. 

Answer D. Praziquantel is the drug of choice for treatment of all fluke (trematode) infections and most tapeworm (cestode) infections. Its antihelminthic action derives from an increase in membrane permeability to Ca, which results in contraction, followed by paralysis, of worm musculature. Mebendazole also has antihelminthic activity, hut it is restricted to the nematodes. The other drugs listed are antiprotozoals. 

The four medically important cestodes are Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm, which can cause cysticerci in the brain and the eyesj, Diphyllobothrium latum (fish tapeworm), and Echinococcus granulosus (dog tapeworm, which can cause hydatid cysts in the liver, lungs, and brain). The primary drugs for treatment of cestode infections are praziquantel (see above) and niclosamide. 

Cestode Infections - The action of the drugs q,uinacrlne and niclosamide... 

Several benzimidazoles are in use for the treatment of helminthic infections. Three of these, mebendazole, thiabendazole and albendazole, are described in this section. They have a broad range of activity against many nematode and cestode parasites, including cutaneous larva migrans, trichinosis, disseminated strongyloidiasis, and visceral larva migrans. A fourth, triclabendazole, is considered as the drug of choice for Easciola hepatica therapy. 

Several other heterocyclic compounds are used as veterinary anthelmintics although they lack the spectrum of activity of the above classes. For example, the antischistosomal drug, praziquantel (14), is highly effective in the treatment of cestodes in animals and man. The piperazine-derived drug diethylcarbamazine (15a) is used as a filaricide and for treatment of lungworm infections in sheep and cattle. The mode of action of diethylcarbamazine (13a) is uncertain but recent studies suggest that an effect on the helminth cuticle may be important. 

Albendazole (Albenza) is primarily used to treat infections caused by the larval form of certain cestodes (tapeworms). These infections often cause cysts (hydatid disease) in the liver, lungs, and other tissues albendazole is used as an adjunct to the surgical removal of these cysts or as the primary treatment if these cysts are inoperable. This drug is also effective against many gastrointestinal roundworms and hookworms, and is typically used as a secondary agent if other anthelmintics are not effective in treating these infections. 

Niclosamide [ni KLOE sa mide] is the drug of choice for most ces-tode (tapeworm) infections. Its action has been ascribed to inhibition of the parasite s mitochondrial anaerobic phosphorylation of ADP which produces usable energy in the form of ATP. The drug is lethal for the cestode s scolex and segments of cestodes but not for the ova. A laxative is administered prior to oral administration of niclosamide. This is done to purge the bowel of all dead segments in order to preclude digestion and liberation of the ova, which may lead to cysticercosis. Alcohol should be avoided within 1 day of niclosamide. 

Worms are known as helminths and the majority is not parasitic. Classes of worms that parasitize man are round worms (nematodes) and flat worms (platyhelminths). The flat worms are divided into tapeworms (cestodes) and flukes (trematodes). Only a few human parasitic worms are common in the United Kingdom, for example threadworms and round worms. In tropical and subtropical parts of the world, where abundant water and high temperatures provide an optimal environment for the larvae and intermediate hosts, parasitic worms are common and widespread. Table 9.8 lists some parasitic worms that can infect man, their effect and drugs used to treat them. 

Praziquantel (PQ) (Table 7-10), a pyrazinoisoquinoline, can be viewed as having evolved from mirasan by optimizing structural features of compound V (Fig. 7-14). For all intents and purposes it is the first really broad-spectrum anthelmintic that is effective against all schistosomes and most other flukes, such as liver, intestinal, and lung (see Table 7-9 for species). PQ is rapidly becoming the drug of choice for many of the preceding infections, as well as for the cestodes (tapeworms). 

THERAPEUTIC USES Praziquantel is FDA approved for therapy of schistosomiasis and liver fluke infections, but also is used to treat infections with many other trematodes and cestodes. Praziquantel is the drug of choice for schistosomiasis caused by all Schistosoma species. Although dosage regimens vary, a single oral dose of 40 mg/kg or three doses of 20 mg/kg each, given 4-6 hours apart, generally produce cure rates of 70-95% and consistent reductions (>85%) in egg counts. Tablets of 600 mg are available. 

Identify the drugs of choice for treatment of common infections caused by nematodes, trematodes, and cestodes. 

Clinical use Mebendazole is a drag of choice for pinworm and whipworm infections. It is one of two drugs of choice (with pyrantel pamoate) for roundworm and for combined infections with ascarids and hookworm. Mebendazole can also be used as a backup drag in certain cestode and trematode infections. Less than 10% of the drag is absorbed systemi-cally after oral use, and this portion is metabolized rapidly. 

Clinical use Niclosamide is one of two drugs of choice (with praziquantel) for infections caused by beef, pork, and fish tapeworm infections. However, it is not effective in cysticer-cosis (for which albendazole or praziquantel is used) or hydatid disease caused by Echinococcus granulosus (for which albendazole is used). Scoleces and cestode segments are killed, but ova are not. Niclosamide is effective in the treatment of infections due to small and large intestinal flukes. 

Niclosamide is often used to treat tapeworm infections since it is usually effective in a single dose. It is minimally absorbed from the gastrointestinal tract and causes few side effects. The drug kills scoleces and cestode segments, but ova are not affected. The answer is (E). 

Anthelmintic important drug for trematode (fluke) and cestode (tapeworm) infections. Increases membrane permeability to Ca causing muscle contraction followed by paralysis. Tox headache, dizziness, GI distress, fever potential abortifacient. 

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