Drugs for Treating Endo and Ectoparasitic Infestations

Adverse hygienic conditions favor human infestation with multicellular organisms (referred to here as parasites). Skin and hair are colonization sites for arthropod ectoparasites, such as insects (lice, fleas) and arachnids (mites). Against these, insecticidal or arachnici-dal agents, respectively, can be used. Endoparasites invade the intestines or even internal organs, and are mostly members of the phyla of flatworms and roundworms. They are combated with anthelmintics.

Anthelmintics. As shown in the table, the newer agents praziquantel and mebendazole are adequate for the treatment of diverse worm diseases. They are generally well tolerated, as are the other agents listed.

Insecticides. Whereas fleas can be effectively dealt with by disinfection of clothes and living quarters, lice and mites require the topical application of insecticides to the infested subject.

Chlorphenothane (DDT) kills insects after absorption of a very small amount, e.g., via foot contact with sprayed surfaces (contact insecticide). The cause of death is nervous system damage and seizures. In humans DDT causes acute neurotoxicity only after absorption of very large amounts. DDT is chemically stable and degraded in the environment and body at extremely slow rates. As a highly lipophilic substance, it accumulates in fat tissues. Widespread use of DDT in pest control has led to its accumulation in food chains to alarming levels. For this reason its use has now been banned in many countries.

Lindane is the active y-isomer of hexachlorocyclohexane. It also exerts a neurotoxic action on insects (as well as humans). Irritation of skin or mucous membranes may occur after topical use. Lindane is active also against intradermal mites (Sarcoptes scabiei, causative agent of scabies), besides lice and fleas. It is more readily degraded than DDT.

Permethrin, a synthetic pyreth-roid, exhibits similar anti-ectoparasitic activity and may be the drug of choice due to its slower cutaneous absorption, fast hydrolytic inactivation, and rapid renal elimination.

Worms (helminths)

Anthelmintic drug of choice

Flatworms (platyhelminths)

tape worms (cestodes) flukes (trematodes) e.g., Schistosoma species (bilharziasis) Roundworms (nematodes)

pinworm (Enterobius vermicularis) whipworm (Trichuris trichiura) Ascaris lumbricoides Trichinella spiralis** Strongyloides stercoralis Hookworm (Necator americanus, and Ancylostoma duodenale)

praziquantel* praziquantel mebendazole or pyrantel pamoate mebendazole mebendazole or pyrantel pamoate mebendazole and thiabendazole thiabendazole mebendazole or pyrantel pamoate mebendazole or pyrantel pamoate

* not for ocular or spinal cord cysticercosis ** [thiabendazole: intestinal phase; mebendazole: tissue phase]

Tapeworms e.g., beef tapeworm

Louse

Spasm, injury of integument

Spasm, injury of integument

Mebendazole
Mebendazole

Trichinella larvae

A. Endo- and ectoparasites: therapeutic agents

Louse

Diuretic Adverse Reactions
Scabies mite
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