Anti-Parasitic & Anthelmintics

Anti-parasitic drugs are used for the treatment of parasitic infections.

Anthelmintics are medications that are used to treat helminths (parasitic worms), such as flukes, tapeworms, roundworms (nematodes). Despite the prevalence of parasitic worms, anthelmintic drug development is unfavourable for the pharmaceutical industry.

Parasitic worms

Hookworm is an intestinal parasite of humans which live in the small intestine. The two main species of hookworm infecting humans are Anclostoma duodenale and Necator americanus.

Ascaris lumbricoides is probably the most common parasitic worm in the world. Ascaris lives in the small intestine and Ascaris eggs are passed in the feces of infected persons.

Pinworm (threadworm) is a small, thin, white nematode called Enterobius vermicularis that sometimes lives in the colon and rectum of humans.

Trichinosis is caused by eating raw or undercooked meat of animals infected with the larvae of a species of roundworm Trichinella.

Whipworm (Trichuris trichiura) infects large intestine. It is spread via the fecal-oral route.

Capillariasis is a parasitic infection caused by two species of nematodes. Capillaria philippinensis causes intestinal capillariasis. Capillaria hepatica is a rare parasite that causes hepatic capillariasis.

Taeniasis is caused by the tapeworm species Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Taenia asiatica (Asian tapeworm). People can become infected with these tapeworms by eating raw or undercooked beef (T. saginata) or pork (T. solium and T. asiatica).

Anthelmintics for parasitic worms

Mebendazole versus Albendazole

Mebendazole and albendazole are benzimidazole derivatives, broad-spectrum anthelmintics. The mechanism of action is blocking glucose uptake in susceptible helminths, thus depleting energy required for their survival.

Mebendazole acts locally in the gut (95% is secreted in the feces) and is excellent at killing parasites that are only in the intestinal tract. Since it is poorly adsorbed from the gastrointestinal tract, mebendazole is not recommended for tissue-dwelling helminth infections such as cysticercosis and hydatid cysts.

However, there is a trade-off between mebendazole's efficacy and safety: due to its poor systemic absorption it is relatively non-toxic. Mebendazole is preferred over albendazole during pregnancy.

Albendazole is better absorbed from the intestine than mebendazole and can reach higher and more effective concentrations in serum. It has an active metabolite albendazole sulfoxide that gets widely distributed in the tissues and cysts. Also, albendazole sulfoxide is active against the larval cestodes. Absorption of albendazole is greatly increased (up to fivefold) if the medication is taken with high-fat foods.

Albendazole can treat heminths that are outside of the intestinal tract such as neurocysticercosis (cysts of tapeworms in the brain) and hyatid cyst.

Hookworm: albendazole is better than mebendazole for treating hookworm [1].

Ascarias (Ascaris lumbricoides, roundworm): both are highly effective against Ascaris, with cure rates of over 97%[2].

Enterobiasis (Enterobius vermicularis, pinworm): mebendazole is preferred antiparasitic in the U.S, albendazole is an alternate drug.

Trichinosis (roundworm Trichinella spiralis): mebendazole is preferred for the treatment of trichinosis.

Trichuriasis (Trichuris trichiura, whipworm): cure rates for trichuriasis are low: 28% for albendazole and 36% for mebendazole. The efficacy is improved by combining mebendazole or albendazole with ivermectin.

Capillariasis: mebendazole is preferred.

Tapeworm (Cestodes): albendazole has an extended spectrum against tapeworms and is therefore the drug of choice in mixed infestation.

• 1. Albonico M, Smith PG, Hall A, Chwaya HM, Alawi KS, Savioli L. Trans R Soc Trop Med Hyg. 1994 Sep-Oct;88(5):585-9.
• 2. Legesse M, Erko B, Medhin G. Ethiop Med J. 2002 Oct;40(4):335-43.
• 3. Parasites Centers for Disease Control and Prevention

Last Updated: September 2011